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.