Professor Nadia Fomin

University of Tennessee

Title: Life and Death of the Free Neutron

Abstract: Modern neutron sources provide extraordinary opportunities to study a wide variety of physics topics, including the physical system of the neutron itself. One of the processes under the microscope, neutron beta decay, is an archetype for all semi-leptonic charged-current weak processes. Precise measurements of the correlation parameters in neutron beta decay as well as the neutron lifetime itself are required for tests of the Standard Model and for searches of new physics. The state of the field will be presented and a program of current and future experiments and potential impacts explored.

Dr. Turgut Yilmaz,
Department of Physics,
University of Connecticut

Topological insulators and their interaction with magnetic impurities and superconductors


Topological properties of materials have recently attracted much attention in the condensed matter physics community due, in part to their possible applications in quantum electronic devices. In particular, topological insulators (TIs) that possess gapless surface states that are topologically protected and can lead to dissipationless quantum electronics. TI's surface state exhibit relativistic momentum dispersion with the Dirac point (DP) located at the time reversal invariant momenta point while the bulk bands are inverted and gapped [1]. Currently, two majority experimental efforts have concentrated on inducing the magnetic and superconducting properties in TI, which would lead to the experimental realizations of quantum anomalous Hall effect (QAHE) and Majorana fermions, respectively [2-3].

Magnetism can be induced in TIs by incorporating impurities into the bulk or on the surface of TIs. If there is a net out-of-plane magnetic moment, an energy gap opens at the DP due to broken time reversal symmetry, which would give rise to QAHE. On the other hand, the superconductivity in can be induced in TI through the proximity effect by growing TIs on the surface of a superconductor. Both, the gapped DP and the superconductivity can be probed by angle-resolve photoemission spectroscopy (ARPES). In this talk, I will present our photoemission studies on the search of broken time reversal symmetry in magnetic TIs and proximity induced superconductivity in TI/superconductor heterostructures. Also, the experimental setup to grow and study TIs at the Physics Department of the University of Connecticut will be presented.

[1] L. Fu, C. L. Kane, and E. J. Mele, Phys. Rev. Lett. 98, 106803 (2007).

[2] X.-L. Qi and S.-C. Zhang, Rev. Mod. Phys. 83, 1057 (2011).

[3] T. Yilmaz, et al., Appl. Surf. Sci. 407, 371 (2017).

Prof. Serge M. Nakhmanson, Department of Materials Science & Engineering, and Institute of Materials Science, University of Connecticut


Mesoscale simulations of ferroic functionalities with finite elements: MOOSE, Ferret and other animals


Ferret is an open-source highly scalable real-space finite-element-method (FEM) based code for simulating transitional behavior of materials systems with coupled physical properties at mesoscale. This code is built on MOOSE, Multiphysics Object Oriented Simulation Environment, and is being developed by a team of collaborators at the University of Connecticut and Argonne National Laboratory. MOOSE allows efficient solving of coupled-physics problems, has a proven record of scaling of execution on up to 10K nodes, and is easily extendable to include new physics and couplings. Real-space FEM approach allows treatment of materials systems possessing complicated geometry and morphology, and evaluation of property dependencies on the system shape, size, microstructure and applied boundary conditions. In this presentation we provide an overview of computational approach utilized by the code, as well as its technical features and the associated software within its tool chain. We also highlight a variety of examples of the code applications, some of which are being pursued in collaboration with a number of different experimental groups. These applications include (a) evaluation of size- and microstructure-dependent elastic and electronic properties of semiconducting core-shell nanostructures; (b) investigation of transitional behavior and topological phases in ferroelectric films, islands, particles and particle-based ferroelectric/dielectic materials; and (c) understanding the workings of photoelectric and electro-optic effects in piezoelectric and ferroelectric materials and nanostructures.

SN acknowledges the efforts of his students John Mangeri, Krishna Chaitanya Pitike and Lukasz Kuna, and senior collaborators S. Pamir Alpay (UConn), and Olle G. Heinonen (ANL), all of whom made major contributions to the projects discussed in this presentation. Funding support from the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program is acknowledged. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for the US Department of Energy. ORISE is managed by ORAU under contract number DE-SC0014664. US National Science Foundation (award number DMR 1309114) is also acknowledged for partial funding of some activities related to the development of the Ferret code.

Dr. Chiara Mingarelli,
Center for Computational Astrophysics, Flatiron Institute


Pulsar Timing Arrays: The Next Window to Open on the Gravitational-Wave Universe


Galaxy mergers are a standard aspect of galaxy formation and evolution, and most (likely all) large galaxies contain supermassive black holes. As part of the merging process, the supermassive black holes should in-spiral together and eventually merge, generating a background of gravitational radiation in the nanohertz to microhertz regime. An array of precisely timed pulsars spread across the sky can form a galactic-scale gravitational wave detector in the nanohertz band. I describe the current efforts to develop and extend the pulsar timing array concept, together with recent limits which have emerged from international efforts to constrain astrophysical phenomena at the heart of supermassive black hole mergers.

Adam Ginsburg, National Radio Astronomy Observatory, Socorro, New Mexico

High mass star and cluster formation

High mass stars are responsible for most of the photons, heavy elements, and energy in galaxies, thereby driving their evolution. They tend to form in dense environments and clusters, which means we can only observe their formation at relatively large distances. I will discuss observational programs, primarily with ALMA, that show how stars form differently in denser parts of galaxies. At higher densities, more stars form in clusters, more stars form in the vicinity of massive stars, and the stellar initial mass function (IMF) shifts to favor higher masses. ALMA data at high resolution show how the feedback from massive stars shapes their environments. The upcoming ALMA-IMF large program will extend this work, showing how the stellar IMF is shaped throughout our Galaxy.

Dr. Aaron LaForge, Department of Physics, University of Connecticut


Excitation dynamics in helium nanodroplets induced by XUV radiation


As opposed to purely molecular systems where electron dynamics proceed only through intramolecular processes, weakly-bound complexes like helium nanodroplets offer an environment where local excitations can interact with neighboring molecules leading to new intermolecular relaxation mechanisms. Here, we present a systematic, time-resolved study of the excitation dynamics when helium nanodroplets are resonantly excited by XUV free electron laser radiation. At low pulse energy, a single atom is excited leading to the formation of a bubble state which relaxes to the droplet surface on a femtosecond timescale. At high pulse energy, a network of excited atoms is formed within a nanodroplets which then collectively autoionizes with high efficiency. Using the pump-probe technique, we were able to time resolve this process.

John Donoghue, UMass Amherst


A possible QFT pathway for UV complete quantum gravity


This is a study of a renormalizable quantum field theory for gravity. It makes use of a gravitational sector which is weakly coupled at all scales, and a helper Yang Mills gauge theory which becomes strong at the Planck scale. While it has an unstable ghost in the propagator, and other unusual properties, unitarity is satisfied at the one loop level as determined by explicit calculation. Further
explorations will be discussed.

22nd Annual Katzenstein Distinguished Lecture

Exploration of the Universe with Gravitational Waves

Professor Rainer Weiss,
Massachusetts Institute of Technology,
2017 Nobel Prize Winner,
Member of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Scientific Collaboration

The observations of gravitational waves from the merger of binary black holes and from a binary neutron star coalescence followed by a set of astronomical measurements is an example of investigating the universe by "multi-messenger" astronomy. Gravitational waves will allow us to observe phenomena we already know in new ways as well as to test General Relativity in the limit of strong gravitational interactions -- the dynamics of massive bodies traveling at relativistic speeds in a highly curved space-time. Since the gravitational waves are due to accelerating masses while electromagnetic waves are caused by accelerating charges, it is reasonable to expect new classes of sources to be detected by gravitational waves as well. The lecture will start with some basic concepts of gravitational waves. Briefly describe the instruments and the methods for data analysis that enable the measurement of gravitational wave strains of 10-21 and then present the results of recent runs. The lecture will end with a vision for the future of gravitational wave astrophysics and astronomy.


Refreshments will be served at 3:00 p.m. outside of GW-38

Dr. Yuya Tanizaki, RIKEN-BNL


Constraints on possible dynamics of QCD by symmetry and anomaly

Low-energy dynamics of Quantum Chromodynamics (QCD) is an important subject for nuclear and hadron physics, but it is a strongly coupled system and difficult to solve. In this situation, symmetry and also anomaly give us an important guide to make a solid conclusion on possible
behaviors of QCD. We will give a brief review on recent development of anomaly matching condition, starting from a simple quantum mechanical example. After that, we explain the newly found anomaly of QCD in chiral limit, and discuss the conclusion of anomaly matching.

Prof. Roger Falcone, University of California, Berkeley

(tentative, to be confirmed)

Title and abstract: forthcoming

Dr. Charlotte A. Mason,
Harvard-Smithsonian Center for Astrophysics

What Can Galaxies Tell Us About Reionization

The reionization of intergalactic hydrogen in the universe's first billion years was likely driven by the first stars and galaxies. The timeline of reionization is currently uncertain but if it is accurately measured it can unveil the properties of 'first light' sources. Lyman alpha (Lyα) emission from galaxies can potentially probe the intergalactic medium (IGM) at high redshifts but requires modeling physics from pc to Gpc scales. I will introduce a new forward-modeling framework which combines cosmological IGM simulations with interstellar medium models to enable Bayesian inference of the IGM neutral hydrogen fraction from observations of Lyα from galaxies. I will present our new measurements of the neutral fraction at z~7 and z~8 and place them in the context of the reionization history. I will describe ongoing efforts with the HST survey GLASS to build larger spectroscopic samples of galaxies at z>6 to further measure the reionization timeline, and future prospects with JWST.

Prof. J. Brad Marston,
Physics Department, Brown University

El Nino as a Topological Insulator: A Surprising Connection Between
Climate and Quantum Physics

Symmetries and topology play central roles in our understanding of physics. Topology, for instance, explains the precise quantization of the
Hall effect and the protection of surface states in topological insulators
against scattering from disorder or bumps. However discrete symmetries and
topology have so far played little role in thinking about the fluid dynamics of oceans and atmospheres. In this talk I show that, as a consequence of the rotation of the Earth that breaks time reversal symmetry, equatorially trapped Kelvin and Yanai waves emerge as
topologically protected edge modes. Thus the oceans and atmosphere of Earth naturally share basic physics with topological insulators. As
equatorially trapped Kelvin waves in the Pacific ocean are an important component of El Nino Southern Oscillation and other climate processes,
these new results demonstrate that topology plays a surprising role in Earth's climate system.

Dr. Jeff Powell,
Department of Physics,
University of Connecticut

Photoelectron emission from metal and dielectric nanoparticles in intense laser fields

Nanoparticles provide a unique platform to study the mechanisms of light interactions with complex systems, in particular, the motion of electrons driven by strong fields and excitation of plasmonic resonances. Here I report on the systematic analysis of the photoelectron emission from single, isolated, gas-phase, spherical nanoparticles as a function of particle size, composition and laser intensity. Gold, silica (SiO2), and silica core/gold shell nanoparticles ranging in size from 5nm to 750nm were irradiated by 800nm, 25fs laser pulses at 0.2-20 TW/cm2 peak intensities. A high energy velocity-map imaging spectrometer was used to determine the cutoff photoelectron energy for each sample and intensity. Nanoparticle size and composition influence the electron cutoff energy, which provides insight into photoelectron trajectories and rescattering dynamics, both of which are affected by near-field enhancement and plasmonic excitation. In particular, I observe that photoelectrons emitted from gold nanoparticles are much more energetic than those from silica, which, in turn, are much faster than those from isolated atoms or molecules exposed to the same light pulses. This work reveals the complex interplay between the external optical field and the induced near-field of the nanoparticle.

Prof. Dawn Meredith, Department of Physics, University of New Hampshire

Instructor and student resources in the physics course for life science students

Over a decade ago, professionals in life science called for the education for the next generation of practitioners to be more interdisciplinary and quantitative. Physicists listened, and in the last decade we have learned a lot about the students and the potential of this course. I will share some insights about what makes this course different from the course for engineers, best practices and new curricula, and the soon-to-be-live Living Physics Portal that provides community and resources for instructors. In the second part of the talk, I'll discuss research that uncovers some productive cognitive resources that life science students bring to the physics classroom on which new understandings can be built.​

Coffee and tea will be served prior to the talk, at 3:00 p.m., In Room GW-103

Prof. Steve Finkelstein, Department of Astronomy,
University of Texas, Austin

Understanding the Reionization of the Universe Now and with JWST


The universe just after the Big Bang was a dark place, while the remnant radiation from the Big Bang cooled, and gas began to pile into dark matter halos. After a few hundred million years, the as-yet unseen first galaxies began to form, and the ionizing radiation produced by their massive stars ionized the intergalactic medium, in a process known as reionization. The search for these first galaxies, and an understanding of the process of reionization, has been a major goal of extragalactic astronomy for decades. While it is commonly assumed that massive stars within star-forming galaxies provide the needed ionizing photons to reionize the intergalactic medium, the commonly assumed ionizing photon escape fractions in the range of 10-50% have thus far exceeded what has been observed (except in a few extreme cases). I will discuss the results of a new semi-empirical model, combining simulated galaxy escape fractions with observed rest-UV galaxy luminosity functions. We find that we can successfully match all observational constraints on reionization by 1) forming stars to physically-motivated halo mass limits; 2) allowing galaxies to be more efficient ionizing photon producers at higher redshift, and 3) allowing a (not strong) contribution from AGNs. This predicts that reionization is a smoother process than previous models, with a predicted volume-averaged ionized fraction of 20% at z=10. JWST will soon dramatically improve our view of the z~10 universe and validate whether significant star-formation is occurring in that epoch, and I will conclude by discussing a recently-approved JWST Early Release Science program which will begin to probe this epoch.

Shany Danieli, Yale University

Hunting low surface brightness galaxies with the Dragonfly Telephoto Array


Dwarf galaxies are a significant component of the galaxy population. Their number density, among other properties, provides strong constraints on theories of galaxy formation, stellar feedback processes, and the distribution and nature of dark matter. However, their low central surface brightnesses makes them difficult to detect and study beyond the Local Group, leading to a biased view of the full galaxy population. To address this problem a new robotic telescope was developed and built, called the Dragonfly Telephoto Array, that is optimized to explore the universe at surface brightness levels below 30 mag/arcsec^2. In this talk I'll describe the technology behind the 1m f/0.4 refractor and present some early results in the dwarf galaxy regime. I will then present our strategy for finding these low surface brightness galaxies as part of the on-going Dragonfly Wide Field Survey that will cover 500 sq. deg. upon survey completion. We will use these data to empirically constrain the Luminosity Function of field galaxies down to the low mass end which is essential for understanding the nature of low-mass dark matter halos.

Shany Danieli is a Physics PhD student at Yale University, working with Prof. Pieter van Dokkum. She specializes in the formation and evolution of dwarf galaxies and Ultra Diffuse Galaxies, both in galaxy groups and in the field (isolated galaxies), using various observational tools such as the Dragonfly Telephoto Array and the Hubble Space Telescope.

Prof. Gerald Dunne, Department of Physics, University of Connecticut

Resurgence and Phase Transitions

Resurgence is a new approach to quantum field theory that combines perturbative and non-perturbative effects in a unified framework. I'll give an overview of the key ideas and discuss applications to phase transitions in physical problems. The main motivation is to find a new way to probe the QCD phase diagram. In this approach, a phase transition is interpreted as a change of dominant saddle in a path integral or partition function. Examples include the Ising model, chiral symmetry breaking in the Gross-Neveu model, the Thirring and Hubbard models, and the large N phase transition in 2d lattice gauge theory.

Dr. Peter D Drummond FAA,
Centre for Quantum and Optical Science, Swinburne University of Technology, Melbourne, Australia

Testing quantum mechanics with modern technology

Wendell Furry [1] and Sydney Coleman [5] were two of Harvard's most original quantum theorists. What can modern quantum technology contribute to their work? Experimentally tested simulations of opto-mechanics[4] and atom interferometers [3], with thermal noise and losses, will be used to analyse proposals for testing Furry's nonlocal decoherence, and Coleman's QFT tunnelling to the true vacuum. Both these ideas are fundamental to our understanding of the quantum universe. Nonlocal decoherence was proposed in Furry's response to Einstein's EPR paper. Today, this idea is becoming testable for massive objects at low temperatures. Entanglement decoherence and massive Schrodinger cats are testable [4] through an optomechanical memory, simulated using the positive-P representation, thus combining technology at Yale and JILA. Coleman's proposal of a false vacuum models fluctuations in the early universe, leading to large-scale structure in the microwave background. Coleman's ideas will be applied to construct a proposal for a laboratory model of the quantum fluctuations in the 'Big Bang', using a coupled BEC experiment in ultracold 41K, simulated with a Wigner phase-space representation [6].

[1] W. H. Furry, Phys. Rev. 49, 393 (1936).

[2] A. Einstein, B. Podolsky, and N. Rosen, Phys. Rev. 47, 777 (1935).

[3] M. Egorov et. al, Phys. Rev. A 84, 021605 (2011).

[4] S. Kiesewetter, R. Y. Teh, P. Drummond and M. Reid, Phys. Rev. Lett. 119, 023601 (2017).

[5] S. Coleman, Phys. Rev. D 15, 2929 (1977).

[6] O. Fialko et. al., J. Phys. B 50 024003 (2017).


Coffee and tea will be served prior to the talk, at 3:00 p.m., In Room GW-103

Jennifer Bergner, Harvard-Smithsonian Center for Astrophysics, Harvard University

Chemical complexity during star and planet formation: new observational and laboratory insights

Planets form by accreting material from a protoplanetary disk, meaning that the inventory of molecules in the disk sets what subsequent chemistry can occur on a newly formed planet. Constraining the organic chemistry in disks and their precursors is therefore key to origins of life studies. I will discuss recent progress in detecting and characterizing simple (HCN and C2H) and complex (CH3CN and HC3N) organic molecules in protoplanetary disks using ALMA, as well as implications for the chemistry at play. As we are sensitivity-limited in the level of molecular complexity that can be detected in disks, observations of organic molecules around low-mass protostars are providing important windows into the initial chemical conditions of disk and planet formation. To complement these observational
approaches, we use laboratory experiments to understand how reactions proceed under conditions of low temperature and low pressure. I will outline our recent work exploring new pathways to chemical complexity in laboratory analogs of
astrophysical ices.

About the speaker: Jennifer Bergner is a graduate student in (Astro)Chemistry at Harvard working with Prof. Karin Oberg at the Harvard-Smithsonian Center for Astrophysics. She is a National Science Foundation graduate research fellow and
specializes in laboratory astrochemistry, focused on the physics and chemistry of interstellar ice analogs.

Dr. Shimshon Kallush,
Physics and Optical Engineering Department, ORT Braude College, Karmiel, and
The Fritz Haber Center for Molecular Dynamics, The Hebrew University, Jerusalem, Israel

Molecular alignment in hot and cold regimes, and its relationship to quantum coherence

The phenomena of field-free instantaneous quantum revivals of molecular alignment and orientation driven by optical and/or terahertz fields will be introduced. A brief survey over a few applications of the phenomena will be presented within this context:

1. Ultracold photoassociation will be shown to intrinsically contain molecular alignment. Its characteristics and the feasibility to detect directional preferences for the photoassociated species will be discussed.

2. Rotational echoes of alignment under multiple pulses will be shown to lead to unique spatial-temporal structures of the refractive index. Several applications of this feature will be suggested.

3. The quantum picture of alignment raises questions that relate to the ability to embed quantum coherences into thermal quantum systems. The problem of quantification of coherences is defined and some results that predict the ability to induce field-driven coherences will be presented

Dr. Ming Li, Department of Physics, University of Connecticut

High Baryon Densities Achievable in the Fragmentation Regions of High Energy Heavy-Ion Collisions

In high energy heavy-ion collisions, the two colliding nuclei pass through each other leaving behind an almost baryon-free central region. Most of the baryon charges are carried away by the receding nuclear remnants. During the collisions, a large amount of kinetic energy is deposited in the central region where a new form of matter called quark-gluon plasma is formed. At the same time, the colliding nuclei are highly compressed, resulting in very high baryon densities in the nuclear remnants. In this talk, I will explore the high baryon density achievable in the nuclear remnants and study the hydrodynamic evolution of the high baryon density matter.

This seminar was originally scheduled for September 10.

Professor Alexandra Pope, Department of Astronomy,
University of Massachusetts Amherst


Rise of dust: Completing our Census of Cosmic Star Formation


Observations at (sub)millimeter wavelengths (~0.25-1.4 mm) provide a unique view of galaxy formation, revealing hidden star formation in the early Universe (a few Gyr after the Big Bang) that cannot be seen at optical wavelengths due to extreme dust obscuration. Previous surveys from single-dish telescopes were sensitive to only the most extreme galaxies forming stars >100 times the rate of the Milky Way, while the more typical galaxies that dominate the total energy budget at these wavelengths remain elusive. I will discuss recent observations of dusty galaxies with the next generation of (sub)millimeter wavelength telescopes -- including the Large Millimeter Telescope (LMT) and the Atacama Large Millimeter Array (ALMA) -- to push studies of dust-obscured activity down to the more typical galaxies that dominate the cosmic star formation history. Finally, I will introduce TolTEC, a revolutionary new camera for the LMT, and the public legacy surveys that will be completed from 2019-2021. These surveys will make a complete census of dust-obscured activity in the Universe.

Coffee and tea will be served prior to the talk, at 3:00 p.m., In Room GW-103 (aka PB-103)

The Physics Graduate Student Association (PGSA) invites all members of the Physics Department to our annual ice cream social event, to introduce our new graduate students and undergraduate majors and welcome everyone back who has recently joined us or returned for the new academic year.

THIS SEMINAR HAS BEEN RESCHEDULED FOR MONDAY, SEPTEMBER 17, 2018

Dr. Ming Li, Department of Physics, University of Connecticut

High Baryon Densities Achievable in the Fragmentation Regions of High Energy Heavy-Ion Collisions

Title: Contributions of Dr. Nora Berrah to the Growth of the Physics Department

Abstract: Dr. Berrah was the Department Head of Physics for the past five years. During that time, she had a major impact on all areas of the department, including important hires in all the major research areas of the department (Particles, Astrophysics, and Nuclear Physics; Atomic, Molecular, and Optical Physics; Condensed Matter Physics), including a new one (Astronomy); encouraging new teaching styles, mentoring early-career faculty, further improving the welcoming climate for undergraduate and graduate students; and raising the profile of the department in the university. Of special interest are four major initiatives she started in Astronomy, Studio Physics, AMO Physics, and Condensed Matter Physics, all of which required considerable effort on her part. In this talk, we will hear about the various hires as well as the four initiatives.

Dr. Marein Rahn, Condensed Matter and Magnet Science Group, Los Alamos National Laboratory

RIXS study of the Anderson Lattice compound
CePd₃


Intermediate valence (IV) materials represent one of the longest standing issues in quantum materials physics [1]. In CePd₃, the correlation of localized and itinerant electrons results in an ambivalent state that strongly fluctuates between the Ce⁴⁺ (4f⁰) and Ce³⁺ (4f¹) configurations. The most striking manifestation of this Kondo hybridization of 4f electrons with a sea of transition metal states occurs at low temperatures, where the valence fluctuations may develop coherency. The few available neutron spectroscopic studies of such coherent "Anderson Lattices" have
revealed that the phenomenon is associated with unusual quasiparticle excitations across the hybridization gap [2]. The low temperature dynamic magnetic susceptibility thus acquires a characteristic energy-/momentum-space texture. The recent advances in soft x-ray resonant inelastic scattering (RIXS) are among the most anticipated developments at 3rd generation synchrotrons. With an energy resolution on the order of E/dE=30000, soft RIXS is now able to address the small energy scale of the IV phenomenon [3]. I present the first use of Ce M-edge RIXS to reveal the evolution of a low temperature coherently hybridized state in CePd₃.

[1] J. M. Lawrence et al., Valence Fluctuation Phenomena, Rep. Prog. Phys 44, 1 (1981)

[2] E. Goremychkin et al., Coherent band excitations in CePd₃, Science 359, 186 (2018)

[3] N. B. Brookes et al., The beamline ID32 at the ESRF, Nuc. Inst. Meth. Phys. Res. Sec. A. 903, 175 (2018)

Fryderyk Lyzwa, Department of Physics, University of Fribourg, Switzerland


Spectroscopic ellipsometry study of LAO/STO (001) heterostructures

The heterostructure LaAlO₃/SrTiO₃ (001) has been intensively studied, after the discovery of a 2-dimensional electron gas forming at its interface [1]. This was surprising since both materials are band-insulators with a relatively high bandgap (>3eV). Moreover, applying a backgate voltage exhibits several phenomena, such as the ability to tune from an insulating into a conducting state [2]. However, the origin of the electric-field effect on this material system is still not understood. In this study, we performed spectroscopic ellipsometry in the mid-infrared region and use the Berreman-mode to analyze the behavior of the conducting layer while applying a backgate voltage.

[1] A. Ohtomo & H. Y. Hwang, Nature 427, 423 (2004)

[2] A. D. Caviglia et. al., Nature 456, 4 (2008)

Connor A. Occhialini, Department of Physics, University of Connecticut


Negative thermal expansion near two structural quantum phase transitions


Recent experimental work has revealed that the unusually strong, isotropic structural negative thermal expansion in cubic perovskite ionic insulator ScF3 occurs in excited states above a ground state tuned very near a structural quantum phase transition, posing a question of fundamental interest as to whether this special circumstance is related to the anomalous behavior. To test this hypothesis, we report an elastic and inelastic x-ray scattering study of a second system Hg2I2 also tuned near a structural quantum phase transition while retaining stoichiometric composition and high crystallinity. We find similar behavior and significant negative thermal expansion below 100 K for dimensions along the body-centered-tetragonal c axis, bolstering the connection between negative thermal expansion and zero-temperature structural transitions. We identify the common traits between these systems and propose a set of materials design principles that can guide discovery of new materials exhibiting negative thermal expansion.


References:

1. Connor A. Occhialini, Sahan U. Handunkanda, Gian G. Guzman-Verri, Jason N. Hancock, "Negative thermal expansion near two structural quantum phase transitions", Frontiers in Physical Chemistry and Chemical Physics (2018)

2. Connor A. Occhialini, Sahan U. Handunkanda, Ayman Said, Sudhir Trivedi, Gian G. Guzman-Verri, Jason N. Hancock, "Negative thermal expansion near two structural quantum phase transitions", Phys. Rev. Materials 1, 070603R (2017)

3. Connor A. Occhilaini, Sahan U. Handunkanda, Erin B. Curry, Jason N. Hancock, "Classical, quantum, and thermodynamics of a model exhibiting structural negative thermal expansion", Phys. Rev. B, 95, 094106 (2017)

4. Sahan U. Handunkanda, Connor A. Occhialini, Ayman H. Said, and Jason N. Hancock, "Two-dimensional nanoscale correlations in the strong negative thermal expansion material ScF3", Phys. Rev. B, 94, 214102 (2016)

Dr. Peter Walter, SLAC National Accelerator Laboratory


The TMO Instrument: Opportunities and Plans for Time-resolved Atomic, Molecular and Optical Science at LCLS-II


The unique capabilities of LCLS, the world's first hard X-ray FEL, have had significant impact on
advancing our understanding across a broad range of science, from fundamental atomic and molecular
physics, to condensed matter, to catalysis and to structural biology.

A major upgrade of the LCLS facility, the LCLS-II project, is now underway. LCLS-II is being developed
as a high-repetition rate X-ray laser with two simultaneously operating, independently tunable
FELs. It features a 4 GeV continuous wave superconducting linac that is capable of producing
uniformly spaced (or programmable) ultrafast X-ray laser pulses at a repetition rate up to 1 MHz spanning the energy range from 0.25 to 5 keV.


The Time resolved AMO (TMO) instrument, one of the four new LCLS-II instruments, will support AMO science, strong-field and nonlinear science, and a new dynamic reaction microscope. TMO will support
many experimental techniques not currently available at LCLS and will locate two experimental endstations. A new reaction microscope endstation will house a COLTRIMS type spectrometer to accommodate extreme vacuum, sub-micron focus spot size, and target purity requirements as dictated by coincidence experiments. The accumulation of data will be performed on an event-by-event basis using the the 1MHz full repetition rate of LCLS-II. A second TMO
endstation will be optimized for performing high energy, high resolution, time- but also angular-resolved
photoelectron spectroscopic measurements. By leveraging its existing suite of spectrometers (i.e. high
resolution iTOF, eTOF, LAMP double-sided VMIs, Kaesdorf spectrometers) a high resolution, high throughput, hemispherical electron analyzer will also be available. The photon fluence at TMO should reach up to 10^22 photons/cm^2, thus allowing to be tailored to specific experimental needs.

This talk will present some of the important science opportunities, new capabilities and instrumentation being planned for NEH 1.1 (TMO) at LCSL-II.

Dale L Smith,
Department of Physics,
University of Connecticut

Velocity Map Imaging of the Single Ionization of
Molecular Iodine

Single ionization in molecules is a critical first step in many higher order process such as high harmonic generation. However, single ionization remains poorly understood even in simple diatomic systems. We have found that molecular iodine, I2, has a complicated ionization processes which does not originate from valance orbitals, as would be expected, but from more tightly bound inner orbitals comprised of 5s electrons. I will discuss two experiments which use ultrafast lasers to investigate the ionization of diatomic I2. Ultrafast laser pulses have a duration in the tens of femtoseconds (fs). Since the vibrational period of I2 is ≈180 fs, we are able to ionize the molecule before it dissociates. Velocity map imaging allows us to observe the kinetic energy release (KER) of charged fragments from dissociation after single ionization. In the first experiment, we have performed a wavelength study from 800 to 400 nm. We have found in the I + I+ dissociation channel (which we denote as the (1,0)) the KER of the fragments was mostly inconsistent with ionization to the X-, A-, or B-states of I2+ which implies ionization through deeper orbitals. A pump-probe Fourier technique also showed that modulation in the cation products only occurs below 0.2 eV, which is consistent with dissociation through the B-state and ionization of high-lying molecular orbitals. This rules out a two-step process through the X- and A-states for much of the observed KER. Employing intensity-, polarization-, and wavelength-dependent experiments we were able to eliminate bond softening, electron rescattering, and photon mediation through the X- or A-states. In the second experiment, we performed a detailed wavelength analysis of I2 around its one-photon B-state resonance at 530 nm where we have identified a strong enhancement in the (1,0) channel. The resonance enhancement is found in both ionization from outer orbitals through the B-state as well as ionization from inner orbitals. Interestingly, the branching ratio for inner orbital ionization reaches over 98% at 519 nm and the peaks in the branching ratios of the two channels occur at slightly different wavelengths. For double ionization into an excited state of I2+ we find that the branching ratio closely follows the branching ratio of the single ionization of deeply bound inner orbitals. This implies that excitation of molecules comes about through inner orbital ionization. The finding of these experiments are inconsistent with current tunneling ionization theory which postulates that ionization arises through the least bound, outer orbital electrons.

Udaya Raj Dahal,
Department of Physics,
University of Connecticut

Polyethylene Oxide Hydration in Solutions, Nanoconfinement and Nanostructures


Amphiphilic water-soluble polymers are actively used in designing novel nanomaterials and have been the subject of extensive experimental and simulation studies. Polyethylene oxide (PEO) is a water soluble, biocompatible, non-toxic synthetic polymer capable of preventing protein adsorption which is widely used in industry and biomedicine for protein crystallization, control of particle aggregation and drug delivery. Most of the applications of PEO and PEO-based nanoparticles are utilized in an aqueous environment as PEO is highly soluble in water due to its ability to form hydrogen bonds with water and therefore understanding the role of water on the conformation and dynamics of PEO and PEO-based nanomaterials is essential in improving and designing new nanomaterials for a variety of applications.

Using all-atom molecular dynamics simulations, we studied PEO in bulk solutions, under nanoconfinement in carbon nanotubes and in nanostructures (PEO brushes grafted to a planar surface and nanoparticles). In the bulk solution, we find that PEO forms a globule like structure in hexane, coil-like structure in water or benzene and an extended rod-like or helical structure is isobutyric acid. The conformation and mobility of PEO in water and in isobutyric acid is dictated by the hydrogen bonding with PEO. As part of our confinement studies, we found that PEO is spontaneously encapsulated from aqueous solution into carbon nanotubes and forms rod-like, helical and wrapped chain conformation depending on the size of the carbon nanotube. The stable helix inside the carbon-nanotube is a consequence of the stable water arrangement around PEO.

As part of our studies of PEO brushes we investigated PEO grafted to gold nanoparticles and planar gold surfaces at varying grafting densities. We found that PEO hydration in the brush depends on grafting density and for gold nanoparticles also varies with the radial distance and nanoparticle radius of curvature. Our simulation results agree well with the classical scaling theories and we were able to explain the curvature dependent hydration based on bulk-solution PEO behavior.

Di Shu, Department of Physics,
University of Connecticut


Threshold Resonance Effects and the Phase-Amplitude Approach


A fundamental aspect of scattering is the appearance of resonances, which are rather ubiquitous. Although their effect is often lost due to averaging at room temperatures or higher, they can become dominant features at low or ultralow temperatures, where only a few partial waves contribute to the scattering process. Our ability to form and manipulate ultracold molecules provides the seed to study in a precise and controlled fashion the role of single partial waves, and state-to-state processes in chemical systems. We will explore resonances occurring due to the existence of a quasi-bound state in the entrance channel of a scattering system and explain the energy scaling due to these near threshold resonances (NTR) based on the properties of the Jost functions. We will also investigate the threshold resonance effects in the Efimov systems which have been studied in a variety of context, such as three-body Coulomb systems and nuclear three-body systems. Numerical schemes based on Milne's phase-amplitude approach are invented to analyze NTR effects. We will present a simple and practical approach to solve the long-standing problem of finding the non-oscillatory solution to Milne's equation. Our numerical approach also gives an integral representation of scattering phase shift and allows us to compute ultra-narrow shape resonances.

Sahan Handunkanda,
Department of Physics, University of Connecticut

Lattice dynamics studies of negative thermal expansion due to two low-temperature lattice instabilities


A material's tendency to shrink upon heating is known as negative thermal expansion (NTE). A class of materials in which the NTE phenomenon arises from the lattice degrees of freedom has gained much attention over the past couple decades. Simple cubic ScF3 is a prominent candidate of this class of materials as it displays strong, isotropic NTE over a 1000 K temperature range. In addition, no structural phase transition has been reported above 0.4K and it retains the simple cubic structure up to its high melting point of 1800 K, which is unusual compared with other transition metal trifluorides.

Here I present a combined inelastic x-ray scattering (IXS), x-ray diffraction (XRD) and thermal diffuse scattering (TDS) study of ScF3, revealing some exciting features of this material such as clean-limit structural quantum phase transition (SQPT), evidence of essential dimensional reduction, disorder phase diagram and nanoscale correlation of NTE modes. Further investigation of the zone center (ZC) dynamics of ScF3 by using infrared (IR) reflectivity measurement reveals evidence of multi-phonon absorption involving low energy NTE modes resides at Brillouin zone boundary. The IR result motivates us to consider a new approach to study NTE dynamics by populating corresponding modes using optical pump. I then address whether the anomalously strong and thermally persistent NTE behavior of ScF3 is a consequence of the SQPT? We carried out an IXS study of a second system Hg2I2 also tuned near SQPT while retaining stoichiometric composition and high crystallinity. We find similar behavior and significant NTE below 100 K for dimensions along the body-centered tetragonal c axis, bolstering the connection between NTE and zero-temperature structural transitions.

Anees Ahmed, Department of Physics, University of Connecticut


Resurgence and Large N: the Gross-Witten-Wadia model


I present a detailed study of parametric resurgence in the Gross-Witten-Wadia unitary model. I show how trans-series expansions in different sectors transmute into each other as they pass through the large N phase transition. This transition is well-studied in the immediate vicinity of the transition point. Here I present a complementary analysis of the transition at all coupling and all finite N, in terms of a differential equation, using the explicit Tracy-Widom mapping of the Gross-Witten-Wadia partition function to a solution of a Painleve III equation. This mapping provides a simple method to generate trans-series expansions in all parameter regimes. A surprising result is uncovered: the strong coupling expansion is convergent and yet there is a non-perturbative trans-series completion. I also define a uniform large N strong-coupling expansion (a non-linear analogue of uniform WKB), which is much more precise than the conventional large N expansion through the transition region, and apply it to the evaluation of Wilson loops and the Beta function.

Dr. Ryan E. Baumbach,
National High Magnetic Field Laboratory, Florida State University

Probing hidden order in URu2Si2: Si → P chemical substitution as a new knob to turn

URu2Si2 persists as a confounding puzzle in condensed matter physics mainly because it hosts an unidentified ordered state ("hidden order") below T0 ≈ 17.6 K and unconventional superconductivity below Tc ≈ 1.5 K. These phenomena occur within a strongly hybridized f-electron lattice that is reminiscent of what is seen for structurally and chemically related systems, many of which which conform to the ubiquitous quantum critical point paradigm. For those materials, superconductivity is associated with quantum fluctuations that emerge as an ordered state (usually magnetic) is suppressed towards zero temperature. This is clearly not the case for URu2Si2, and various measurements show that (1) hidden order does not have an intrinsic magnetic moment and (2) the superconductivity is completely enclosed by hidden order. A multitude of theories have been proposed to describe this behavior, but no consensus has been reached regarding their success. In order to elucidate this situation we have tuned URu2Si2 using electronic shell filling (Si → P), where rich phenomena are observed. Importantly, both hidden order and superconductivity are replaced by heavy fermion metallic behavior without any ordering for chemical substitutions of less than 2%. Even as the ground state abruptly changes, the high temperature strongly hybridized correlated electron lattice remains close to its virgin state. In order to further expose this evolution, we have carried out Shubnikov de Haas quantum oscillation measurements probing the Fermi surface and charge carrier effective masses in the x region where hidden order is destroyed. I will discuss how these results may provide a window into the hidden order puzzle and their implications for different models of URu2Si2.

Dr. Christian Weiss, Jefferson Lab


Next-generation nuclear physics with polarized light ions at EIC


The future Electron-Ion Collider (EIC) will enable next-generation experiments in high-energy electron scattering on protons and nuclei, including polarized light ions (deuteron, 3He, ...). Such measurements address important physics topics such as the spin structure of the neutron, effects of nuclear interactions on the quark/gluon densities, and coherent phenomena in QCD at small x. Detection of the nuclear breakup following the high-energy process ("spectator nucleon tagging") reveals the nuclear configurations present during the high-energy process and permits a controlled theoretical treatment of nuclear effects. We present an overview of the physics objectives, theoretical methods, experimental techniques, and on-going R&D efforts related to measurements with polarized deuteron beams and spectator nucleon tagging at the EIC. We present new results in the theory of nuclear final-state interactions, diffraction and nuclear shadowing, and polarization phenomena in deep-inelastic scattering with spectator tagging. We give a perspective on future physics studies and detailed process simulations for the EIC.

Prof. Gerald Dunne, Department of Physics, University of Connecticut


Stephen Hawking: His Life and His Physics


Stephen Hawking was arguably the best known scientist of the past 50 years. He had a far-reaching impact both on the public appreciation of science and also on advanced research in theoretical physics and cosmology. This talk will review his life and his major scientific achievements, primarily concerning the remarkable properties of black holes. The talk will be quite general, accessible to a wide audience.


Coffee will be served prior to the talk, at 3:00 p.m., In Room P-103

Luke Kelley, Astronomy and Astrophysics, Harvard University

LIGO has now detected Gravitational Waves (GW) from numerous, stellar-mass black-hole binary systems. Pulsar Timing Arrays can use the incredibly precise radio flashes from pulsars to measure GW from binaries of supermassive black-holes (SMBH). We use state-of-the-art, cosmological hydrodynamic-simulations ("Illustris") to model the mergers of galaxies and the SMBH they host. In this talk, I will outline the key physical processes which mediate the SMBH-binary merger process, and present our predictions for the GW signals that Pulsar Timing Arrays will observe. I will highlight the physical information about SMBH & SMBH-environments encoded in those GW signals, and discuss how long we'll have to wait for the first detections in this exciting new regime.

Luke Kelley is a finishing PhD student in the Harvard Astronomy Department, working with Prof. Lars Hernquist on Massive Black-Hole Binaries using data from the Illustris cosmological simulations. Luke's work makes important predictions for gravitational wave signals detectable by Pulsar Timing Arrays in the next decade. If you would like to meet with Luke, please email Cara Battersby (cara.battersby@uconn.edu) to set up a time.

Dr. Maitri Warusawithana,
Department of Physics,
University of North Florida


Emergent New Electronic
Properties in Atomic Layer Complex Oxide Superlattices

Complex oxides exhibit a plethora of collective phenomena such as ferroelectricity, magnetism and superconductivity.
They have been widely studied both in bulk and thin film form. Advances in synthesis techniques have enabled the
formation of atomically precise interfaces between isostructural complex oxide phases with different ground states. Using ozone-assisted molecular beam epitaxy we synthesize such superlattices with sharp interfaces at the atomic layer limit. I will discuss two examples where the interfaces lead to novel electronic properties that do not exist in the bulk constituent phases: asymmetric ferroelectricity in three-component superlattices of titanate phases, and modified
electronic and magnetic properties in ordered pseudo alloys of mixed-valent manganites.

Dr. Robert R. Jones, Department of Physics, University of Virginia


Controlled Transfer of Electronic Wavepacket Motion Between Distant Atoms


The establishment, observation, and potential control of correlated multi-electron dynamics is a complex problem of interest across disciplines with numerous applications in a variety of contexts, from femtosecond interatomic Coulomb decay and attosecond charge migration within small molecules, to energy transfer in photosynthetic systems, to quantum control of few- and many-body systems, and quantum information processing. The extreme sensitivity of Rydberg atoms to electric fields, including those produced by neighboring atoms, makes them superb candidates for studying such phenomena. In a quantum analogy to classical far-field radio transmission from a source to receiver antenna, we have transferred electronic wavepacket motion established within Rydberg atoms in a dilute nearly-frozen gas to neighboring Rydberg atoms. The transfer is enabled by electron correlations resulting from electric field-controlled, atom-atom couplings and relies on the use of both cold atom and ultrafast techniques.

Dr. Yibo Yang, Department of Physics and Astronomy, Michigan State University

A glimpse of the proton spin through lattice

Deep-inelastic scattering experiments reveal that contrary to the naive quark model, the quark spin contribution to the proton spin is quite small, about 30%. In an effort to search for the missing proton spin, recent analyses of the high-statistics 2009 STAR experiments at RHIC showed evidence of non-zero glue helicity in the proton. However, the results are limited by very large uncertainty in the x < 0.05
region.

To address this issue from the theoretical side, we made the first lattice QCD calculation of the glue spin in the proton based on the LaMET framework, and the results suggested that a large part of the missing component of the proton spin comes from the gluon spin. The results on the other parts of the proton spin will be also presented.

UConn Physics Colloquium


A celebration in recognition of Professor Douglas Hamilton's teaching, scholarship, and service


We will come together to honor Professor Douglas Hamilton upon the occasion of his retirement from teaching, scholarship, and academic service at the University of Connecticut. The colloquium will open with remarks, recollections and anecdotal observations concerning Doug's 39-year academic career at UConn by his former doctoral students, colleagues, and associates. Time permitting, Doug will reflect on some of the highlights of his experiences and accomplishments.

Jason Hancock
with organization by Dave Perry


Friday, April 20, 2018
3:30 p.m.
Gant Science Complex
Physics, Room PB-38

Refreshments will be served prior to the talk at 2:30 p.m. in Room P-103

Scott Galica, Department of Physics, University of Connecticut


Polychromatic Optical Forces in Diatomic Systems


This dissertation discusses an experiment to demonstrate the application of the stimulated bichromatic optical force (BCF) on the diatomic molecule calcium monofluoride (CaF). The research demonstrates the deflection of a supersonic beam of CaF through the application of BCF under a variety of conditions, highlighting distinctive characteristics of the force. Results show that the measured deflection of the molecular beam is consistent with the behavior of BCF under the tested conditions. In particular, we have measured a predicted reversal in the direction of the force as well as an applied force which exceeds the radiation pressure force. Detailed modeling of the BCF in multilevel systems corroborates our findings. We discuss the development and application of these models with respect to non-ideal conditions present in the experiment. The construction of the molecular beam source and BCF laser systems are discussed in detail. A brief discussion of further modeled extensions of the BCF through the addition of higher order sidebands is presented as well. Overall, our results demonstrate that the BCF is a potentially useful tool for the manipulation of cold molecules.

Fridah Mokaya, Department of Physics, University of Connecticut

High Statistics Analysis of All-Neutral Decays of Vector Mesons with the Radphi Experiment


The differential cross section and spin density matrix elements for ω(782) meson photoproduction in the reaction 9Be(γp, pω)8Li have been measured in the energy range 4.4 - 5.4 GeV using the Radphi detector. Radphi used a 9Be target, and identified the final state by triggering on the recoil proton plus neutrals. At the kinematics of this experiment, the observed nuclear cross section is consistent with the γp cross section measured by prior experiments when multiplied by 4 for the number of protons in the nucleus, in agreement with a naive spectator model. However, the spin observables show some deviation from a spectator model, particularly approaching the low-t limit of the experimental acceptance. Besides the cross sections, spin density matrix elements in Gottfried Jackson and Helicity frame have been measured. The data selection is discussed and the acceptance is examined and quantified. The results are compared to a model for vector photoproduction.

Dr. Erica Nelson,
Harvard-Smithsonian Center for Astrophysics,
Harvard University

The Emergence of Galactic Structure


I will discuss the emergence of galactic structure: how the Universe evolved from its uniform state shortly after the Big Bang to the rich diversity of galaxies today. Despite having determined the primary structural building blocks that comprise local galaxies -- bulges and disks -- we still do not know how they formed. The improved spatial resolution with which we can now observe early galaxies has given us a clearer window into how they grew. Combining millimeter interferometry, near infrared integral field spectroscopy, and cosmological hydrodynamical simulations, I will discuss new insights into the formation of disks and bulges at the peak epoch of star formation.

Yiteng Tian, University of Connecticut

Stochastic Tomography: Characterizing Small-scale Heterogeneity in Earth Using Coherence Functions


This thesis work presents a thorough study of stochastic tomography technique, from theory to numerical validation and application in characterizing small-scale heterogeneity in Earth's mantle using a statistical approach. Fluctuations in amplitude and travel time of teleseismic P waves, measured by amplitude and phase coherence beneath elements of EarthScope seismic array, are used to invert for the heterogeneity spectrum of P velocity in a 1000 km thick region of the upper mantle beneath the array. Best fits to joint transverse coherence functions require a depth-dependent heterogeneity spectrum, with peaks in narrow depth ranges that agree well with the predictions for a temperature derivative of velocity that includes the effects of chemical and phase variations expected for standard models of the silicate mineral assemblage of the upper mantle. The results confirm the existence of significant chemical as well as thermal contributions to observed upper mantle heterogeneity at spatial scales between 50 km to 300 km.

Prof. Dominik Schneble,
Department of Physics and Astronomy, Stony Brook University


Exploring the Physics of Spontaneous Emission in a Matter-Wave Open Quantum System


The question how irreversibility can emerge in quantum mechanics is central to the study of open quantum systems. A simple example is the exponential decay of an excited two-level atom as described by the Wigner-Weisskopf model of
quantum optics, in which spontaneous photon emission is sometimes viewed as being driven by fluctuations of the
surrounding vacuum. However, the Markov approximation underlying this model can be violated under certain conditions, and recent experiments on optical decay in photonic bandgap materials have indeed started to find deviations from its predictions.

We have recently realized an "artificial atom" in which the excited-state energy and the vacuum coupling can be
controlled at will, thus allowing for a systematic exploration of spontaneous emission beyond the Markov
approximation. Naively, a two-level atom may be viewed as a photon trap that is empty or full; we instead realize a microscopic trap for a single atom that can decay, under coherent external driving, by emitting the atom into the
surrounding vacuum. The experiments are performed using an optical lattice geometry that provides arrays of such artificial atoms coupled to a one-dimensional matter waveguide. In my talk I will present experimental results on Markovian and strongly non-Markovian dynamics, including exponential and partly reversible oscillatory decay, atom reabsorption, as well as a bound state for emission below the edge of the mode continuum that features an evanescent matter wave and which is the direct analog of the long-predicted atom-photon bound state in photonic bandgap
materials. I will conclude with an outlook on future applications of our system in open-system many-body quantum
physics.

Prof. Abbas Ourmazd, University of Wisconsin-Milwaukee


Don't be a control freak.


At weddings, the bridal photo is taken under bright lights, with the happy couple holding still. Traditionally in science, the "best" observations are those with the largest signal from the most tightly controlled system. Like bridal photos, the results are not always exciting. In a wide range of phenomena -- from the dance of proteins during their function, to the breaking of molecular bonds on the femtosecond scale -- tight control is neither possible, nor desirable. Modern data-analytical techniques extract far more information from random sightings than usually obtained from set-piece experiments.

I will describe on-going efforts to extract structural and dynamical information from noisy, random snapshots recorded with very poor, or non-existent timing information. Examples will include conformational dynamics of molecular machines, and the ultrafast dynamics of bond-breaking.

Less can be more, but only if there is plenty of it.

In collaboration with: J. Copperman, A. Dashti, R. Fung, A. Hosseinizadeh, G. Mashayekhi, M. Schmidt, P. Schwander (UWM); J. Frank et al. (Columbia), des George et al. (CUNY), B. Hogue et al. (ASU), R. Santra et al. (CEFL), Aquila et al. (SLAC).


Coffee will be served prior to the talk, at 3:00 p.m., In Room P-103

Ekaterina Sergan,
Physics Department.
University of Connecticut


Enhanced Harmonic Generation with Ultra-short Laser Pulses


Table top short-pulsed UV lasers are coveted for their usefulness in time-resolved studies of molecular dynamics. However, current wave-mixing and harmonic generation techniques using crystals fail to preserve the short pulse unless the crystal is made thin, thus limiting the conversion efficiency. The alternative is to focus the fundamental beam into a gas, but the phase shift accumulated by a Gaussian beam as it propagates through the focus leads to destructive interference of the generated harmonics. This work presents two methods to alleviate this issue through use of a semi-infinite geometry for third harmonic generation. The first method involves placing a metal septum at the waist such that the laser drills a small pinhole, which in turn disrupts the beam after the waist. The second method uses a very thin septum as a separator for two gases: one with a large third order susceptibility (before the focus), and the other with a small susceptibility (after the focus). Both methods inhibit harmonic generation immediately after the beam waist. Experiments with third harmonic generation lead to increased conversion efficiency and better mode quality, and had the appropriate perturbative behavior. Simulations supported the experimental results and were used to explore limitations on generation. The techniques were extended to fifth harmonic generation. Although an improved spectrum was observed, increased conversion efficiency was not observed in the experiment. Moreover, simulations indicated that fifth harmonic light production is due to wave-mixing, not generation. Finally, simulations with Bessel-like beams are described as an alternative method for future experiments.

Dr. Ian Stephens,
Harvard-Smithsonian Center for Astrophysics,
Harvard University


Trying to Make Sense of Polarization Patterns in Circumstellar Disks


In the era of ALMA, we can now resolve polarization within circumstellar disks at (sub)millimeter wavelengths. While we initially hoped that these observations would give us insight on magnetic fields within disks, the observed polarization patterns indicate other possible mechanisms may polarize the signal. These mechanisms include polarization from scattering and emission from grains aligned with the radiation anisotropy. Can we make sense of all these disk polarization observations? In this presentation, I will show many polarization observations toward disks, and I will discuss the theoretical expectations for different polarization mechanisms. Hopefully, the answer to the question will be an astounding "Yes!"

Dr. Daniel Mazzone, National Synchrotron Light Source II, Brookhaven National Laboratory


Intertwined degrees of freedom in the series Nd1-xCexCoIn5


Strongly correlated electron systems are quantum materials that reveal a deep intertwining between different electronic charge, orbital, spin and lattice degrees of freedom. The interaction among them can stabilize ground states that feature novel collective phenomena. Particular complex phases occur in systems containing rare earth elements, where the conduction electrons either screen or couple the magnetic moments of partially filled electronic f-states. The subtle balance between these energy scales yields strong electronic fluctuations that trigger a rich diversity of states including unconventional superconductivity, antiferromagnetism or correlated insulating, metallic and topological protected states.

It is an open question how magnetic order is affected when the local f-electrons become itinerant. While the prevailing theory predicts the possibility of two separated critical points, it is unknown whether they have an impact on the magnetic structure. I will present our recent results on the evolution of magnetic order in the series Nd1-xCexCoIn5 that features a Kondo breakdown within an antiferromagnetic phase. We find a transition between two distinct magnetic phases that is detached from the emergence of heavy-bands, demonstrating that the magnetism and the Kondo coupling can be governed by different energy scales. The observation of two magnetic structures with different symmetry is evidence that the magnetic interactions change with increasing electronic itineracy. This opens novel perspectives for the fundamental understanding of the microscopic mechanism controlling the various quantum phases in this class of materials.

We further investigated the intertwined degrees of freedom in the itinerant limit of the series. CeCoIn5 is a paramagnetic heavy-fermion with a d-wave superconducting ground state that is believed to be mediated by magnetic fluctuations. The superconducting condensate features an additional phase at very low temperatures and large magnetic fields. This so-called Q-phase reveals magnetic order that only survives inside the superconducting condensate and directly couples to it. I will show that the Q-phase is stable under a perturbation 5% Nd doping, and that the high-field phase is separated from a low-field antiferromagnetic state via a magnetic instability that may origin from a field-induced quantum phase transition. Intriguingly, both phases display an identical magnetic symmetry, which prevents the emergence of a primary order parameter of magnetic nature in the Q-phase. We suggest the presence of an auxiliary superconducting order parameter in the Q-phase that couples magnetic order with d-wave superconductivity. This is in contrast to the behavior in the low-field phase, where we believe that superconductivity and magnetism remain decoupled.

Dr. Mark S. Hybertsen,
Center for Functional Nanomaterials, Brookhaven National Laboratory

Single Molecule Junction Conductance & Force Measurements: Laboratory to Probe Structure-Function Relationships

The break-junction technique for simultaneous measurement of junction conductance and sustained force in single molecule junctions bridging metal electrodes naturally probes a large ensemble of junction realizations. The histogram of measured quantities, such as the rupture force or the junction conductance, represent results for ensembles that inherently sample diverse and distinct junction structures at the nano scale [1]. For each structure, conductance and sustained force as a function of junction elongation is sampled for a span of distance defined by stochastic events, particularly the bond rupture event. This rich data set probes structure-function relationships with a stochastic sampling of structure at the nanoscale. In this talk I will discuss these measurements from the theorist perspective with supporting models and calculations. I will also discuss the potential for modeling the data for each individual junction in the ensemble, focusing on sampling the link bond energy [2].

[1] M. S. Hybertsen and L. Venkataraman, Acc. Chem. Res. 49, 452, 2016.

[2] M. S. Hybertsen, J. Chem. Phys. 146, 092323, 2017


Coffee will be served prior to the talk, at 3:00 p.m., In Room P-103

Jonathan Hudson,
Physics Department.
University of Connecticut


D-terms in Bosonic and Fermionic Systems


The D-term is a fundamental particle property which is defined through the matrix elements of the energy-momentum tensor and as such in principle on equal footing with mass and spin. Yet the D-term is experimentally not known for any particle. In this thesis the D-terms of bosons and fermions are studied. It is shown that the D-term of a spin-0 boson is D = -1in free theory. This value is modified by even infinitesimally small interactions in Φ^4 theory. This shows how sensitive the D-term is to the dynamics of the theory. It is shown that the property D = -1 is preserved when the boson is not point-like but given a finite size. The situation is fundamentally different for a spin 1/2 fermion, where the D-term vanishes in the free field case. On the example of the bag model it is shown how a fermionic D-term can be generated by interactions.

Xiang Zhang,
Department of Physics,
University of Connecticut

Study of Supercontinuum and High Repetition Rate Short Pulse Generation



The rapidly increasing data traffic nowadays has benefited a lot from the dramatic progress of optical telecommunications such as dense wavelength division multiplexing (DWDM) and time-division multiplexing (TDM), which employ broadband light source and high-repetition ultrashort optical pulse respectively to carry information in optical fibers. High speed all optical data processing and switching components will also be important in future fiber-optic communication systems since conventional electro-optical parts have reached their bottleneck both speed-wise and efficiency-wise. In this PhD thesis work, I propose a dispersion varying scheme realized by non-uniformly tapering fibers or waveguides to enhance supercontinuum generation. The physical mechanism to generate broadband continuum such as dispersion, nonlinearity, and soliton dynamics have been explained. Numerical demonstration has been done in both lead silicate microstructured optical fibers and chalcogenide planar waveguides. A fiber ring laser system with rational harmonic mode-locking and nonlinear polarization rotation of a highly nonlinear photonic crystal fiber has been designed and experimentally demonstrated to generate stable ultrashort optical pulse train at a repetition rate of 30 GHz with low signal noise ratio. All-optical encryption operating at 250 Gb/s using optical Boolean logical gates based on the two-photon absorption (TPA) in bulk semiconductor optical amplifiers (SOAs) has been demonstrated. The effects of TPA on the performance of optical logical gates based on quantum-dot SOAs has also been explored. TPA can improve the operating speed up to 320 Gb/s.

Sadiq Rangwala,
Raman Research Institute, India

Refrigeration of ions with atoms

Advances in cooling and trapping for several distinct species of atoms, ions and molecules have gone hand-in-hand for a long time now. Cold dilute gas ensembles to single particle realization of these have led to investigations of diverse problems in many body physics and exotic physics on one hand to unprecedented spectroscopic precision on the other. In most cases, it is the interaction between trapped particles and the confining fields which is used to realize the system of interest. In these systems, it is typical to know the initial position and motional state with precision. Most experiments though are performed with either atoms or ions or molecules.

Combining cold ions, atoms and molecules for experiments has been gaining traction in recent times. Such combined hybrid traps [1] pose very specific challenges for simultaneous trapping and cooling of the multiple species. In addition the interactions between different species become paramount and it is imperative to understand how the combined systems evolve, how energy is exchanged, what is the final state mediated by these interactions, etc. Of course very important work on this topic has been pioneered at U. Conn. In this talk I shall present our experimental system which can simultaneously cool and trap, within a cavity mode, atoms, ion and molecules in any combination [2]. In this experiment interactions between co-trapped species whose long range interaction range from 1/r to 1/r6 can be probed. I shall then present results of how an ion in a Paul trap is cooled by a MOT of atoms. The details of the cooling hold several surprises such that the ultimate temperature of the trapped ions can be decided by the spatial size of the MOT [3,4], the process of resonant charge exchange is very effective of ion cooling [5], etc. I shall conclude with the prospects of experiments in the future, with such ion-atom systems at ultracold temperatures.


References:

[1] K. Ravi, S. Lee, A. Sharma, G. Werth, and S. A. Rangwala, Appl. Phys. B 107, 971 (2012).

[2] S. Jyothi, T. Ray, N. B. Ram, and S. A. Rangwala, in Ion Traps Tomorrow's Applications (IOS Press, 2015), 189, 269--278.

[3] K. Ravi, S. Lee, A. Sharma, G. Werth, and S. A. Rangwala, Nat. Commun. 3, 1126 (2012).

[4] S. Dutta, R. Sawant, and S. A. Rangwala, Phys. Rev. Lett. 118, 113401 (2017).

[5] S. Dutta and S. A. Rangwala, arXiv:1705.07572

Prof. Wen-Fai Fong,
Department of Physics and Astronomy, Northwestern University

The detection of gravitational waves and light from the same cosmic source has become one of the most highly-anticipated discoveries in physics and astronomy. Thanks to the recent onset of Advanced LIGO/Virgo, on August 17, 2017, this discovery came to fruition with the first direct detection of a merger of two neutron stars, followed by the detection of electromagnetic emission across ten orders of magnitude in wavelength. The merger, termed GW170817, was localized to a galaxy in our own cosmic neighborhood, allowing us to study the properties of the merger and its environment in unprecedented detail. Here, I describe efforts to localize GW170817 and uncover its properties through gravitational wave and electromagnetic observations. I also discuss the host galaxy and broad properties of GW170817 in the context of cosmological short gamma-ray bursts. Finally, I concentrate on open questions raised by GW170817 and the bright future ahead for multi-messenger astronomy.


Coffee will be served prior to the talk, at 3:00 p.m., In Room P-103

Dr. Chelsea L. MacLeod,
Harvard--Smithsonian Center for Astrophysics, Harvard University

Fast and Furious: Understanding the Changing-Look Quasars

Quasars, or active galactic nuclei (AGN), emit copious broadband radiation from the environment surrounding their
central supermassive black holes. In the "changing look quasars", rare and spectacular drops or jumps in quasar luminosity occur on timescales far shorter than expected, as discovered from repeat photometric and spectroscopic observations in this dawning era of time domain astronomy. I present results from spectroscopic follow-up of highly variable quasars in a quest to understand these objects.

Professor Takaaki Kajita of the Institute for Cosmic Ray Research at the University of Tokyo and 2015 Nobel Prize recipient will be speaking on Oscillating Neutrinos

"Neutrinos have been assumed to have no mass. It was predicted that, if they have masses, they could change their type while they propagate. This phenomena is called neutrino oscillations. Neutrino oscillations was discovered by deep underground neutrino experiments. I will describe the discovery of neutrino oscillations and the implications of the small neutrino masses. The status and the future neutrino oscillation studies will also be described."

Dr. Betsy Mills, Department of Astronomy, Boston University

Journey to the center of the Galaxy: following gas accretion from hundreds of parsecs to the black hole

The central 300 pc of the Milky Way is a reservoir of hot and turbulent dense gas that surrounds, and may in the future feed, a quiescent supermassive black hole. Fully constraining the physical conditions of this gas is critical for understanding how this central gas concentration will evolve, and influence future nuclear activity. I will present the results of my recent work following the changes in physical properties of this gas as it approaches the black hole; increasing in temperature, density, and turbulence, while largely resisting the onset of star formation. This is the strongest evidence yet that the extreme gas conditions in this region are driven by accretion and infall processes. One of the greatest remaining challenges in relating the physical conditions of the gas with its location in the central potential is our edge-on view of this region, which complicates the determination of 3D positions. I will discuss prospects for better constraining Galactocentric distance in this environment and testing current orbital models. I will also address future prospects for measuring the infall rate as a function of radius in this region. Finally, as there is a limit to the conclusions that can be drawn from just one galaxy nucleus, I will preview the
advances in our understanding of gas accretion in nuclei that are now possible via comparisons to high resolution ALMA
observations of the center of NGC 253, a galaxy with an order of magnitude more star formation and molecular gas,
where this gas is not only accreting but also outflowing.

Coffee will be served prior to the talk, at 3:00 p.m., In Room P-103

Prof. Emily Myers, Dept. of Speech, Language, and Hearing Sciences, University of Connecticut

There's many a slip twixt ear and lip: distortions, discontinuities, and disasters in speech perception

The sounds of speech are as complex as they are biologically important. Fine-grained differences in the acoustics of speech allow the listener to understand the difference between bears and pears, and between uncles and ankles. Over a lifetime of experience with our native language, we develop exquisite sensitivity to some acoustic contrasts, yet lose the ability to perceive other distinctions, including some speech contrasts in other languages. The result is that our perceptual experience does not veridically reflect the acoustics of the speech stream. Work from my lab and others suggests that the brain copes with the complexity of the speech signal by integrating information from context online to guide perception when the speech signal is ambiguous. Further, with sufficient training, listeners can overcome the perceptual barriers established during development and make inroads in distinguishing novel speech sound contrasts.


Coffee will be served prior to the talk, at 3:00 p.m., In Room P-103

Dr. Clay Tabor,
Department of Geography,
University of Connecticut

Understanding orbitally driven δ^{18}O variability in the South Asian monsoon region

Speleothem records suggest that there has been significant long-term climate variability in the South Asian Summer Monsoon (SASM) region related to Milankovitch cycles. These records are difficult to interpret because their oxygen isotopic signals can represent several different climate responses. Here, I use an Earth system model with water isotope tracers to directly simulate the isotopic data captured in the speleothems. From these model simulations, I show that a large portion of the orbital signal found in the speleothem records is due to changes in the amount of water vapor coming from different sources. When India receives relatively less insolation in the summer months, most of the local precipitation sources from the nearby ocean. Conversely, when India receives relatively more insolation in the summer months, a greater portion of the local precipitation sources from farther away. Changes in the amount of local evaporation compared to precipitation also have an important effect on the isotopic signals found in the SASM speleothem records.

Coffee will be served prior to the talk, at 3:00 p.m., In Room P-103

Niloy Dutta, Department of Physics, University of Connecticut

Optical Transmission and Fiber Lasers

This talk will describe our research over the last few years in the area of fiber lasers, supercontinuum generation, optical correlation and optical transmission studies. Future directions in these areas will be discussed

Prof. Or Hen, Department of Physics, MIT

Fluctuating Nucleons in Asymmetric Nuclei

The atomic nucleus is one of the most complex strongly-interacting many-body Fermionic systems in nature. A main challenge in describing nuclei is understanding the short interparticle part of the nuclear wave function. Recent high-energy proton and electron scattering experiments show that short-range interactions between the nucleons form
correlated, high-momentum, neutron-proton pairs, known as Short-Range Correlations (SRC). There measurements suggest that these correlations account for 20% of the nucleons in the nucleus, and 60-70% of the kinetic energy carried by nucleons in nuclei, thereby having large implications to the modification of the bound nucleon structure function and more.

In this talk I will overview the experimental studies of SRC in nuclei with emphasis on new results on asymmetric
nuclei and intriguing developments of effective theories for short-range physics that follow the experimental results.
Given time I will also discuss some of the wide-ranging the implications of SRCs for various phenomena, including the isospin dependence of the bound nucleon wave function, the nuclear symmetry energy and the structure of neutron stars and more.

Coffee will be served prior to the talk, at 3:00 p.m., In Room P-103

Dr. Anne Jaskot,
Department of Astronomy,
University of Massachusetts Amherst

How to Reionize the Universe - Clues from the Green Pea Galaxies

In the first billion years after the Big Bang, the universe's hydrogen gas became ionized, an event known as reionization. Reionization represents a fundamental transition in the universe's properties, and yet, we know little about how it occurred. The most likely explanation is that ionizing, Lyman continuum (LyC) photons escaped into the intergalactic medium from early star-forming galaxies. However, most star-forming galaxies show no sign of LyC escape. If reionization was caused by galaxies, which galaxies were responsible? The recent discovery of escaping ionizing radiation from the unusual "Green Pea" galaxies has provided new clues to this puzzle. I will discuss what we are learning from the Green Peas about how ionizing radiation escapes galaxies and about the possible properties of the galaxies that reionized the universe.

Derrek Wilson, Department of Physics, Kansas State University

The scaling of strong field interactions with wavelength

An important aspect of light-matter interactions is their dependence on the frequency of the light. In the ultrafast, strong-field regime, the wavelength can be responsible for how matter responds to an intense field, governing phenomena related to the dynamics of accelerating free (or quasi-free) electrons. In this presentation, I will discuss two studies whose aims are to answer questions on the role wavelength in strong field interactions.

In the first study, we will look into strong field absorption in solid state materials, which have been shown to depend on the density of states. We consider the role of wavelength on this process by scanning across an octave of central wavelengths, covering two photon and three photon absorption for Gallium Arsenide. When varying the density of states, we see that the response changes with wavelength. Our current explanation is based on the dynamics of the electron in the conduction band, with longer wavelengths capable of inducing Bragg reflections more readily.

The second project shows progress on a light source suitable of studying strong field science in the long wave infrared (LWIR). The source, which is based on difference frequency generation of an optical parametric amplifier, is capable of generating few-cycle pulses with central wavelengths spanning 5-9 microns, and peak intensities in the 100 TW/cm^2 region. As a proof of principle for this sources ability to extend strong field science into the LWIR, we perform strong field ionization of Xenon gas across this wavelength range.

Dr. Paul Torrey,
NASA Hubble Postdoctoral Fellow,
Massachusetts Institute of Technology


Probing Galaxy Formation with Modern Cosmological Simulations


Cosmological simulations are among the most powerful tools available to probe the non-linear regime of cosmic
structure formation. They also provide a clear test-bed for understanding the impact that hydrodynamics and feedback processes have on the evolution of galaxies. I will present results from the recent Illustris and IllustrisTNG simulations with a focus on the evolution of cosmic metals. Illustris and IllustrisTNG are detailed galaxy formation simulations that reproduce important observations such as the galaxy stellar mass function, cosmic star formation rate density, and galaxy morphological diversity. I will briefly overview the numerical framework, discuss the key physical model ingredients, and explore in detail the cosmic coevolution of galaxies and their metals. After reviewing some of the basic results, I will show that Illustris broadly reproduces the observed fundamental
metallicity relation and argue that this relation alone may allow us to discriminate between bursty and non-bursty feedback models with JWST.

Dr. Wiewei Xie, Louisiana State University

Chemistry Perspectives to Design New Quantum Materials

New solid-state materials with exotic physical properties are imperative by forming a basis for most of the critical key technology of today's information society. In this talk, I will describe some empirical design rules and examples that have yielded new quantum materials (superconductors, superconductors with non-trivial band topology, and topological materials) from the viewpoint of chemistry.

Dr. Meg Urry,
Department of Physics and Astronomy, Yale University


Does Supermassive Black Hole Growth Affect Galaxy Evolution?


As galaxies evolve, their rates of star formation change dramatically. Theorists have suggested that energy released by Active Galactic Nuclei (which are rapidly growing supermassive black holes at galaxy centers) could quench star formation, and that AGN episodes are triggered by major galaxy mergers. Having conducted a comprehensive census of supermassive black hole growth using multiwavelength surveys, we looked for evidence that merger-induced AGN shut down star formation, for the first time using morphological information to encode the merger history. Both in the local universe and 7-9 billion years ago (at the peak of star formation and black hole growth), we find some evidence that AGN play a role, especially at earlier times and for higher mass galaxies. However, at both epochs most galaxies are disk-dominated, indicating little role for major mergers, and they evolve too slowly for AGN to play a significant role. Instead, halo mass may cut off the accretion of gas onto the galaxy, thus quenching stellar growth passively.


Coffee will be served prior to the talk, at 3:00 p.m., In Room P-103

Shiqi Yin,
Department of Physics,
University of Connecticut

Magnetic and magnetocaloric properties of rare earth chromites bulk powders and thin films

As a safe, efficient, and environmentally friendly technology, magnetic refrigeration is an alternative solution to conventional vapor compression technology and requires materials with large magnetocaloric effect (MCE), such as rare-earth chromites (RCrO3). In this dissertation, the structural, magnetic, and magnetocaloric properties of bulk HoCrO3 has been investigated. In order to improve MCE, HoCrO3 samples with different particle sizes were synthesized and sample with smaller particle size shows larger MCE. Furthermore, Ho1-xGdxCrO3 (x=0, 0.33, 0.67, and 1) solid solutions were explored, and their structural, magnetic, and magnetocaloric properties show systematic change versus
the substitution ratio x. Gd substitution considerably improves MCE of HoCrO3 and pure GdCrO3 bulk sample shows larger MCE than any other reported RMnO3, RCrO3, and RFeO3 bulk powder samples. Besides, a clear understanding of change with ionic radius, structural distortion on the magnetic and magnetocaloric properties of HoCrO3 were achieved by Tm
(smaller ionic radii) and Gd (larger ionic radii) doping on the A-site. Gd doping increases the magnetic transition temperature of Cr3+ (TN) and Tm doping decreases . The application of external hydrostatic pressure was found to enhance TN of HoCrO3, similar to the effect of Gd substitution. In addition, HoCrO3 thin films were fabricated via a solution route on platinized silicon substrates and characterized by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. By doping Fe at the B-site, the HoCr0.7Fe0.3O3 films show larger TN than the HoCrO3
films. The large MCE in HoCrO3 bulk system, along with its tunability by particle size or chemical doping, make it suitable for magnetic refrigeration in low temperature region (below 30 K).

Soroush Khosravi-Dehaghi,
Department of Physics,
University of Connecticut


Femtosecond nonlinear optical spectroscopy of carotenoids and single wall carbon nanotubes


Nonlinear optical spectroscopy can provide the most comprehensive picture of the optical response of any quantum system. The energy structure and excited state dynamics of the system can be revealed unambiguously, using such a comprehensive time- and frequency- resolved (both detection and excitation frequencies) optical response. My research has been focused on the measurement and interpretation of the optical responses of different samples using two of the most advanced ultrafast nonlinear optical spectroscopy techniques including Transient Absorption (TA) and Transient Grating (TG) spectroscopies. Transient absorption spectroscopy measures the time- and frequency- resolved (detection) amplitude of the optical response of the system after an initial excitation to a specific energy state. Heterodyne transient grating spectroscopy, which employs a more sophisticated light-matter interaction geometry, measures the phase of the optical response in addition to its time- and frequency- resolved (detection) amplitude. The latest results of the measurements on carotenoids and single wall carbon nanotubes (SWNTs) will be presented.

Zhiwei Zhang,
Department of Physics,
University of Connecticut

Electronic orders in superoxygenated cuprates and nickelates

I will present a study of the electronic orders in three superoxygenated samples, La2CuO4+y, La1.94Sr0.06CuO4+y and Pr2NiO4+y using resonant x-ray scattering. Charge order has not been found for over a decade in the superoxygenated lanthanum cuprates though reported in most of other similar systems. The phase separation property of this system raises the difficulty in investigating charge order. This defense will present evidence for the existence of charge order in our La2CuO4+y sample. The La1.94Sr0.06CuO4+y shows no charge order, but a special structural tilt never reported before. The results for Pr2NiO4+y suggests nematicity related to charge order and structural tilts as reported in some recent reports.

Dr. Allison Kirkpatrick, Department of Astronomy, Yale University


Dusty Star Forming Galaxies in the Distant Universe

At z = 1 − 3, the formation of new stars is dominated by massive, dusty galaxies, whose far-IR emission indicates they contain colder dust than their counterparts in the local Universe. I explore the reasons for the evolving IR emission of similar galaxies over cosmic time using three samples of dusty galaxies. Despite similar infrared luminosities, z >0.5 dusty star forming galaxies have an order of magnitude higher dust masses and 5 K colder dust temperatures. The increase in dust mass is linked with an increase in the gas fractions of dusty star forming galaxies with redshift. I find that dusty star forming galaxies are predominantly located on the main sequence at z=1-2, and I explore whether an active galactic nucleus is linked with declining star formation in these galaxies. Finally, I make predictions for
the demographics of dusty galaxies that we will be able to observe with the James Webb Space Telescope at z=1-2.

Prof. Thomas Weinacht, Physics Department, Stony Brook University,


Non-adiabatic dynamics in strong field molecular ionization

I will describe a series of experiments that study strong field molecular ionization with coincidence velocity map imaging as a function of pulse duration and pulse shape. The measurements, in conjunction with electronic structure and quantum dynamics calculations, reveal a subtle interplay between electronic and nuclear dynamics underlying the population of multiple states of the molecular cation.

Suchitra Sebastian, Cavendish Laboratory, Cambridge University

Exploring Materials Universes

Materials comprise trillions of electrons that interact with each other to create a diversity of physical behaviours. We owe much of modern technology - from powerful computing to the marvels of communication - to discoveries of new types of collective electron behaviours in materials. Such discoveries, however, are often serendipitous, given that materials can be thought of as complex universes teeming with vast numbers of electrons, making their behaviours challenging to understand or predict. A question we are often confronted with is how to make progress in discovering novel collective electron behaviours akin to new universes. I will discuss possible approaches to increasing the odds of making discoveries, with examples from cases such as new superconductors and new types of dual metal-insulating materials.


Coffee will be served prior to the talk, at 2:30 p.m., In Room P-103

Please notice the new colloquium time.

Dr. Pierre Pillet,
Laboratoire Aime Cotton, CNRS, Univ Paris-Sud, ENS Paris-Saclay


Cold dense and disordered gases with strong dipole-dipole coupling


Dipole-dipole long-range interactions between two atoms in dense and cold atomic media play a crucial role in many physical configurations by considering ground state atoms as well as highly-excited Rydberg atoms. They may alter the coherent scattering of light. They open also many opportunities for studying few-body and many-body physics, and hopefully for simulating many different quantum systems.

Two examples will be discussed: the scattering light by a microscopic cold and dense atomic cloud, and the quantum thermalization of a frozen Rydberg gas in Förster coupling.

Anna Pancoast, TBA

Solving the complex problems that we face in our world today requires a more talented workforce
than we have ever needed before. Such a workforce must be comprised of a wide range of diverse
talents and creative insights. No segment of the population can be ignored or overlooked in this
talent search. This presentation will describe the most recent research that demonstrates the
positive impact that social and informational diversity has on science and scholarly advancement,
the reasons for this impact and the importance of committed leadership in achieving a strong,
supportive and inclusive workplace where creativity and productivity is maximized.

Adil-Gerai Kussow,
Department of Physics, University of Massachusetts, Lowell

Quasiparticles in a periodic crystal lattice from two-particle electronic excitations: many-electron fermionic wave function

A novel first-principle theory of the quasiparticles in a periodic crystal lattice described in terms of two-particle electronic excitations has been formulated. The many-electronic system is treated as an ensemble of two-electron excitations which describe the electron-electron scatterings in the field of the core ions. This concept is an alternative to the one-electron effective field approach and neither the density-functional formalism nor the semiclassical electron gas model are utilized. The many-electron wave function, which provides, due to the fermionic antisymmetry embedded, the full description of the electronic exchange-correlation effects, is calculated. Based on
the non-perturbative Green Function method, in a unified manner, both the ground and the excitation states of a
lattice, with any degree of the exchange-correlation interactions, are evaluated. It is shown that this scheme, if compared with Hedin GW, considerably simplifies the calculation of the quasiparticle energies.