Physicists used to think that superconductivity – electricity flowing without resistance or loss – was an all or nothing phenomenon. But new evidence suggests that it’s not so clear cut, at least in copper oxide superconductors. “If we understood why copper oxide is a superconductor at such high temperatures, we might be able to synthesize a better one”, says UConn physicist Ilya Sochnikov. Sochnikov and his colleagues at Rice University, Brookhaven National Lab and Yale recently figured out part of that puzzle, and they report their results in the latest issue of Nature.[Read More]
PhD student Lukasz Kuna and undergraduate Hope Whitelock participate in a symposium “Mesoscopic phenomena in ceramic materials” arranged by Materials Scientist Serge Nakhmanson at the “Electronic and Advanced Materials Conference” in Orlando, Florida. Four UConn students including Tulsi Patel, Krishna Chaitanya Pitike, Lukasz Kuna and Hope Whitlock showcased their research.[Read More]
Whoever said rules were made to be broken wasn’t a physicist. When something doesn’t act the way you think it should, either the rules are wrong, or there’s new physics to be discovered. Which is exactly what UConn’s Connor Occhialini ’18 (CLAS), an honors student majoring in physics and math, found when he began researching scandium fluoride. Most materials swell as they heat up. Scandium fluoride must be doing something else, reasoned Occhialini. […][Read More]
John Mangeri’s Award Lands Him in Argonne National Laboratory John Mangeri (left) with his SCGSR-award host Dr. Olle Heinonen (right) in front of the Chemistry building (bldg. 200) at Argonne National Laboratory. (Photo credit to Dr. Andrea Jokisaari) By Katherine Eastman John Mangeri, a Ph.D. candidate in Dr. Serge Nakhmanson’s “Complex Materials by Computational Design” […][Read More]
Dr. Sochnikov is a recipient of Montana Instruments Cold Science Exploration Awards Lab Startup Grant. Dr. Ilya Sochnikov has just started new scanning SQUID microscopy lab at the University of Connecticut. Ilya Sochnikov’s research focuses on nanoscale quantum phenomena in new materials. An emergence of a new phenomenon or a phase transition occurs when interactions […][Read More]
October 6, 2015 – Kim Krieger – UConn Communications Jason Hancock, Assistant Professor in Physics, with graduate students, Erin Curry and Sahan Handunkanda, have been investigating a substance that shrinks when it warms. Most materials swell when they warm, and shrink when they cool. But UConn physicist Jason Hancock has been investigating a substance that responds in reverse: […][Read More]
March 26, 2015 – Tim Miller Researchers have made an experimental breakthrough in explaining a rare property of an exotic magnetic material, potentially opening a path to a host of new technologies. From information storage to magnetic refrigeration, many of tomorrow’s most promising innovations rely on sophisticated magnetic materials, and this discovery opens the door to harnessing […][Read More]
Prof. J. Haraldsen, University of North Florida , "Examining multi-band effects on the electronic compressibility of a 2D electron gas: Insights into the negative compressibility of LAO/STO", Condensed Matter Physics Seminar11:00am
Prof. J. Haraldsen, University of North Florida , "Examining multi-band effects on the electronic compressibility of a 2D electron gas: Insights into the negative compressibility of LAO/STO", Condensed Matter Physics Seminar
Wednesday, February 3rd, 2021
11:00 AM - 12:00 PM
Storrs Campus onlineProf. J. Haraldsen, University of North Florida
Examining multi-band effects on the electronic compressibility of a 2D electron gas: Insights into the negative compressibility of LAO/STO
In this study, we investigate the consequences of two electronic bands at the negative electronic compressibility (NEC) cross-over point for a two-dimensional electron gas (2DEG) using a simple homogeneous model with Coulombic interactions and first-order multi-band coupling. We examine the role of effective mass and relative permittivity in relation to the critical carrier density at the cross-over point through a comparison of one- and two-band models. In general, it is shown that the population of a second band, along with the presence of inter-band coupling, can dramatically change the cross-over carrier density. Given the difficulty in determining and confirming multi-band electronic systems, this model provides a potential method for identifying multi-band electronic systems using precise bulk electronic properties measurements. To help illustrate this method, we apply our results to the observed NEC in the 2D electron gas at the interface of LaAlO3/SrTiO3 (LAO/STO) and determine that, for the known parameters of LAO/STO, the system is likely a realization of a two-band 2D electron gas. Furthermore, we provide general limits on the inter-band coupling with respect to the electronic band population.
Zoom link: https://kth-se.zoom.us/j/62759109592
Condensed Matter Physics Seminar10:00am
Tuesday, December 8th, 2020
10:00 AM - 11:00 AM
Storrs Campus onlinePeter Littlewood, University of Chicago
Dynamical phase transitions at many body exceptional point
Spontaneous synchronization is at the core of many natural phenomena. Your heartbeat is maintained because cells contract in a synchronous wave; some bird species synchronize their motion into flocks; quantum synchronization is responsible for laser action and superconductivity. The transition to synchrony, or between states of different patterns of synchrony, is a dynamical phase transition that has much in common with conventional phase transitions of state -- for example solid to liquid, or magnetism -- but the striking feature of driven dynamical systems is that the components are "active". Consequently quantum systems with dissipation and decay are described by non-Hermitian Hamiltonians, and active matter can abandon Newton's third law and have non-reciprocal interactions. This substantially changes the character of many-degree-of-freedom dynamical phase transitions and the critical phenomena in their vicinity, since the critical point is an "exceptional point" where eigenvalues become degenerate and eigenvectors coalesce. We will illustrate this in several different systems -- a Bose-Einstein condensate of polaritons, models of multicomponent active matter such as flocks of birds, generalised Kuramoto models, and others. We argue that there is a systematic theory, generalized phase diagram, and corresponding universality classes for these dynamical systems.
Fruchart et al., arXiv:2003.13176
Hanai et al., 10.1103/PhysRevLett.122.185301
Zoom Meeting: https://kth-se.zoom.us/j/67773156040
Prof. Sang Wook Cheong, Department of Physics and Astronomy, Rutgers University, "Trompe L'oeil Ferromagnetism", Condensed Matter Physics Seminar9:30am
Prof. Sang Wook Cheong, Department of Physics and Astronomy, Rutgers University, "Trompe L'oeil Ferromagnetism", Condensed Matter Physics Seminar
Monday, November 30th, 2020
09:30 AM - 10:30 AM
Storrs Campus onlineProf. Sang Wook Cheong,
Department of Physics and Astronomy, Rutgers University
Trompe L'oeil Ferromagnetism
The characteristics of ferro-(ferri)magnetism with non-zero magnetization include magnetic attraction, magnetic circular dichroism, and magneto-optical Kerr (MOKE), Faraday, and various anomalous Hall-type (Hall, Ettingshausen, Nernst, and thermal Hall) effects. Non-magnetic or antiferromagnetic materials in external electric fields or other environments (called specimen constituents) can share symmetry operational similarity (SOS) with magnetization in relation to broken symmetries. These specimen constituents can be associated with non-zero magnetization and/or show ferromagnetism-like behaviors, so we say that they exhibit Trompe L'oeil Ferromagnetism. Examples include linear magnetoelectric materials such as Cr2O3 under electric fields, Faraday effect in chiral materials such as tellurium with current flow, magnetic field induced by the motion of Neel- or Bloch-type ferroelectric walls, and magneto-optical Kerr (MOKE), Faraday effect, and/or anomalous Hall-type effects in certain antiferromagnets such as Cr2O3, MnPSe3, Mn4(Nb,Ta)2O9, and Mn3(Sn,Ge,Ga). A large number of new specimen constitutes having SOS with Magnetization will be discussed, and require future experimental verification of their ferromagnetism-like behaviors, and also theoretical understanding of possible microscopic mechanisms.
We will have two presentations and by Los Alamos theorists:, Condensed Matter Physics Seminar9:30am
Tuesday, November 24th, 2020
09:30 AM - 11:00 AM
Storrs Campus onlineWe will have two presentations and by Los Alamos theorists:
9:30-10:00 Shizeng Lin (Los Alamos)
Switching of valley polarization and topology in twisted bilayer graphene by electric currents
The associated manuscript is available at https://arxiv.org/abs/2002.02611.
10:00-10:30 Jian Xin Zhu (Los Alamos)
Signatures of Spin Polarized Fermi Arcs in the Quasiparticle Interferences of CeBi
Professor Saroj Prasad Dash, Quantum Device Physics Laboratory, Dept. Microtechnology and Nanoscience, Chalmers University of Technology, Sweden, "Spin Current in Topological Quantum Materials", Condensed Matter Physics Seminar10:00am
Professor Saroj Prasad Dash, Quantum Device Physics Laboratory, Dept. Microtechnology and Nanoscience, Chalmers University of Technology, Sweden, "Spin Current in Topological Quantum Materials", Condensed Matter Physics Seminar
Tuesday, November 10th, 2020
10:00 AM - 11:00 AM
Storrs Campus onlineProfessor Saroj Prasad Dash,
Quantum Device Physics Laboratory, Dept. Microtechnology and Nanoscience,
Chalmers University of Technology, Sweden
Spin Current in Topological Quantum Materials
An outstanding feature of topological quantum materials is their unique spin topology in the electronic band structures with an expected novel charge‐to‐spin conversion effects. In the Weyl semimetal candidate WTe2 we observed both conventional1 and unconventional2 charge‐to‐spin conversion effects at room temperature. In addition to the conventional spin Hall and Rashba--Edelstein effects, we also measured an unconventional charge‐to‐spin conversion component in WTe2. Such a large spin polarization can be possible in WTe2 due to a reduced crystal symmetry combined with its large spin Berry curvature, spin--orbit interaction with a novel spin‐texture of the Fermi states. We also investigated giant Rashba spin-orbit materials BiTeBr to detect the current induced spin polarization at room temperature.3 Furthermore, we integrated graphene with a topological insulator4,5 in van der Waals heterostructures6 to engineer proximity-induced spin-charge conversion phenomena. In these heterostructures, we experimentally demonstrate a gate-tunable spin-galvanic effect at room temperature, allowing for efficient conversion of a non-equilibrium spin polarization into a transverse charge current.7 These findings provide an efficient route for realizing all-electrical and gate-tunable spin phenomenon in topological materials and their heterostructures.
1. Observation of charge to spin conversion in Weyl semimetal at room temperature.
B Zhao, D Khokhriakov, Y Zhang, H Fu, B Karpiak, AM Hoque, X Xu, Y Jiang, B Yan, SP Dash.
Physical Review Research 2 (1), 013286 (2020).
2. Unconventional charge-to-spin conversion Weyl Semimetal WTe2. B Zhao, B Karpiak, D Khokhriakov, A Johansson, AM Hoque, X Xu, Y Jiang, I Mertig, SP Dash. Advanced Materials, 2000818 (2020).
3. Electrically controlled spin injection from giant Rashba spin-orbit conductor BiTeBr"
Z Kovács-Krausz et al., Nano Letters 20, 7, 4782--4791 (2020).
4. Origin and evolution of surface spin current in topological insulators
A Dankert, P Bhaskar, D Khokhriakov, IH Rodrigues, B Karpiak, MV Kamalakar, S Charpentier, I Garate, SP Dash.
Phys. Rev. B 97, 125414 (2018).
5. Room Temperature Electrical Detection of Spin Polarization in Topological Insulators
A Dankert, J. Geur, M.V. Kamalakar, SP Dash;
Nano Letters 15 (12) 7976 (2015).
6. Tailoring emergent spin phenomena in Dirac material heterostructures.
D Khokhriakov, A. W. Cummings, K Song, M Vila, B Karpiak, A Dankert, S Roche and SP. Dash.
Science Advances, 4, 9, eaat9349 (2018)
7. Gate-tunable Spin-Galvanic Effect in Graphene - Topological insulator van der Waals Heterostructures at Room Temperature. D Khokhriakov, AM Hoque, B Ka
Prof Jeremy Levy, Department of Physics and Astronomy, University of Pittsburgh, "Ferroelastic Textures, Magnetism, and Superconductivity in LaAlO3/SrTiO3", Condensed Matter Physics Seminar10:00am
Prof Jeremy Levy, Department of Physics and Astronomy, University of Pittsburgh, "Ferroelastic Textures, Magnetism, and Superconductivity in LaAlO3/SrTiO3", Condensed Matter Physics Seminar
Tuesday, November 3rd, 2020
10:00 AM - 11:00 AM
Storrs Campus onlineProf Jeremy Levy, Department of Physics and Astronomy, University of Pittsburgh
Ferroelastic Textures, Magnetism, and Superconductivity in LaAlO3/SrTiO3
LaAlO3/SrTiO3 heterostructures exhibit a wide range of phenomena that are not well understood. The most prominent are the existence of superconductivity at very low densities, which has been known for more than half a century, and magnetism, which is a more recent discovery. Here I will review experiments that directly probe and/or control these effects at nanoscale dimensions, and suggest that there are strong couplings between ferroelastic domain structure (texture) in LaAlO3/SrTiO3 and both magnetism and superconductivity. I will also examine a connection between some reports of magnetism in transport experiments and phenomena related to superconductivity.
Dr. D. Farfurnik, University of Maryland, "Enhancing the coherence properties of quantum dots toward quantum photonic applications", Condensed Matter Physics Seminar10:00am
Dr. D. Farfurnik, University of Maryland, "Enhancing the coherence properties of quantum dots toward quantum photonic applications", Condensed Matter Physics Seminar
Tuesday, July 14th, 2020
10:00 AM - 11:00 AM
Storrs Campus onlineDr. D. Farfurnik, University of Maryland
Enhancing the coherence properties of quantum dots toward quantum photonic applications
Self-assembled Quantum Dots (QD) exhibit some of the best single photon emission properties, including nearly ideal efficiency and indistinguishability. As such, and considering their compatibility with nanofabrication techniques, on-chip integration of QDs as single photon emitters and non-linear components plays a key role in integrated photonic-based information processing and may pave the way toward the creation of quantum networks. Manipulating and storing quantum information utilizing QD spins, however, is limited by their short coherence times originating from interactions with a nuclear bath. In this talk, I will describe our approaches for addressing this challenge: First, the application of dynamical decoupling (DD) pulse sequences prolongs the coherence times by decoupling the QD spins from the environment. While the performance of such protocols is often limited by the accumulation of pulse imperfections, arbitrary spin control enabling composite and concatenated sequencing could further enhance the achievable spin control fidelities . Such a sequencing is implementable by driving a Lambda system of the QD utilizing an optical signal arbitrarily modulated by a temperature-stabilized electro optical modulator (EOM). I will present a recent experimental demonstration of such a control , our analysis for optimizing the EOM working point for enhancing the achievable optical rotation Rabi frequencies, as well as the efficiency of the protocol for QDs strongly coupled to L3 photonic crystal cavities. Second, the resulting coherence properties may be further enhanced by utilizing molecules of coupled QDs (QDM), which offer a singlet-triplet ground state decoherence-free subspace . Beyond the promising combination of such a subspace with the application of DD sequences, leveraging the isolated optical transitions of the QDM may offer single-shot spin readout capabilities. I will present our approach for implementing such a spin readout incorporating microwave pi-pulses, its experimental feasibility utilizing optimally designed transmission lines, and the expected readout fidelities based on the achievable microwave Rabi frequencies .
 D. Farfurnik et al., ``Optimizing a dynamical decoupling protocol for solid-state electronic spin ensembles in diamond'', Phys. Rev. B 92, 060301(R) (2015)
 J.H. Bodey et al., ``Optical spin locking of a solid-state qubit'', npj Quantum Information 5, 95 (2019)
 D. Kim et al., ``Ultrafast optical control of entanglement between two quantum-dot spins'', Nat. Phys. 7, 223--229 (2011)
 D. Farfurnik et al., ``Experimental realization of time-dependent phase-modulated continuous dynamical decoupling'', Phys. Rev. A 96, 013850 (2017)
Zoom Meeting: https://kth-se.zoom.us/j/61809414846
Prof. L. Levitov, Department of Physics, MIT, "Long-Lived Excitations, Directional Memory and Hydrodynamic Transport in Two-Dimensional Electron Fluids", Condensed Matter Physics Seminar9:00am
Prof. L. Levitov, Department of Physics, MIT, "Long-Lived Excitations, Directional Memory and Hydrodynamic Transport in Two-Dimensional Electron Fluids", Condensed Matter Physics Seminar
Friday, April 10th, 2020
09:00 AM - 10:00 AM
Storrs Campus onlineProf. L. Levitov, Department of Physics, MIT
Long-Lived Excitations, Directional Memory and Hydrodynamic Transport in Two-Dimensional Electron Fluids
It was found recently that 2D electron fluids can support collective excitations that are not subject to Landau's \(T^2\) dissipation [1,2,3]. This surprising behavior originates from the head-on carrier collisions, a process that dominates angular relaxation at not-too-high temperatures \(T \ll T_F\) due to the joint effect of Pauli blocking and kinematic constraints. As a result, a large family of exceptionally long-lived excitations emerges, associated with the odd-parity harmonics of momentum distribution. This leads to "tomographic" dynamics: fast 1D spatial diffusion along the unchanging velocity direction accompanied by a slow angular dynamics that gradually randomizes velocity orientation. The abnormally slow angular relaxation originates from correlated angular dynamics involving "lock-step'' angular displacements along the Fermi surface occurring in collinear two-particle collisions. The slow loss of directional memory is described as non-Brownian angular random walk, "superdiffusion" on the Fermi surface. The collective behavior with directional memory dominates at moderately long times, pushing the onset of conventional hydrodynamics to abnormally large timescales. The tomographic regime features an unusual hierarchy of time and length scales, resulting in scale-dependent transport coefficients. The scale dependence manifests itself in fractional-power current flow profiles and unusual conductance scaling vs. temperature and sample size. This exotic behavior can be directly probed by transport measurement techniques, as well as by momentum-resolved tunneling measurements.
1. P J Ledwith, H Guo, L Levitov, The Hierarchy of Excitation Lifetimes in Two-Dimensional Fermi Gases,
Annals of Physics 411, 167913 (2019)
2. P J Ledwith, H Guo, A V Shytov, L Levitov,
Tomographic Dynamics and Scale-Dependent Viscosity in Two-Dimensional Electron Systems,
Phys Rev Lett 123, 116601 (2019)
3. P J Ledwith, H Guo, L Levitov, Angular Dynamics and Directional Memory in Two-Dimensional Electron Fluids,
Zoom Meeting: https://kth-se.zoom.us/j/123036826
CANCELLED:, Dr. J. Nathan Hohman, Institute of Materials Science and the Department of Chemistry, University of Connecticut, CANCELLED: Condensed Matter Physics Seminar2:00pm
CANCELLED:, Dr. J. Nathan Hohman, Institute of Materials Science and the Department of Chemistry, University of Connecticut, CANCELLED: Condensed Matter Physics Seminar
Tuesday, March 17th, 2020
02:00 PM - 03:00 PM
Storrs Campus GS 119CANCELLED:
Dr. J. Nathan Hohman,
Institute of Materials Science and the Department of Chemistry, University of Connecticut
Self-Assembly of Low-Dimensional Nanomaterials in Crystalline Ensemble
When reduced in size to the nanoscale, materials express compelling new phenomena. For example, a single layer abstracted from graphite leads to fantastic new properties in graphene, or a nanocrystal of gold takes on new optical properties as a nanoparticle. Making materials very small or very thin has been an easy way to prepare exciting new materials--for example, the 2D transition metal dichalcogenides (TMDCs) have a long history of investigation prior to the recent interest in their monolayers for applications in photovoltaics, electrocatalysts, and spintronic materials. 2D phases have been uncovered for a number of elements and binary semiconductors, although many compounds do not share the same propensity to form 2D structures. Through the use of hybrid materials like hybrid perovskites and metal organic chalcogenide assemblies (MOCHAs), low-dimensional nanostructures can be prepared that are part of a crystalline ensemble, unlocking new portions of the period table to the exploration of low-dimensional phases. Importantly, hybrid materials combine organic components which enables structural and electronic direction at the molecular scale. Here, we consider the structure and organization of mithrene- silver benzeneselenolate- a self-assembling layered hybrid structure, and examine its optoelectronic properties in the context of a 2D-like material. Synthetic manipulation of dimensionality and topology is used to prepare a family of related crystalline polymer systems, and the role of intermolecular forces and molecular geometry on the inorganic phases are considered in the context of transitions between 1D, 2D, and 3D coordination polymer systems.
Contact Information: Prof. B. WellsMore
Dr. Sumanta Bandyopadhyay, Nordita, "Superconductivity in a nonhermitian system and Berezinksii classification ", Condensed Matter Physics Seminar2:00pm
Dr. Sumanta Bandyopadhyay, Nordita, "Superconductivity in a nonhermitian system and Berezinksii classification ", Condensed Matter Physics Seminar
Wednesday, March 11th, 2020
02:00 PM - 03:00 PM
Storrs Campus GS 119Dr. Sumanta Bandyopadhyay,
Superconductivity in a nonhermitian system and Berezinksii classification
We have investigated the effects of nonhemriticty on superconducting states. Nonhermiticity enters our system due to electrons leaking out of/into (in case of pumping) the system. We have explicitly constructed several unconventional pairing amplitudes in nonhermitian systems in thep resence and absence of the particle-hole symmetry. We find nonhermitian dynamics induces odd frequency superconducting states, and we present the related experimental observables. We have further studied the robustness of the Berezinskii classification  of anomalous pairing amplitude in the presence of the nonhermiticity and shown that SP∗OT∗=−1 symmetry withstands nonhermiticity.
CANCELLED:, Dr. A. B. Belonoshko, Department of Physics, Royal Institute of Technology, Sweden, CANCELLED: Condensed Matter Physics Seminar2:00pm
CANCELLED:, Dr. A. B. Belonoshko, Department of Physics, Royal Institute of Technology, Sweden, CANCELLED: Condensed Matter Physics Seminar
Tuesday, March 10th, 2020
02:00 PM - 03:00 PM
Storrs Campus GS 119CANCELLED:
Dr. A. B. Belonoshko,
Department of Physics, Royal Institute of Technology, Sweden
Iron under extreme conditions
I will report the latest theoretical data on the iron phase diagram. A particular emphasis will be on the stabilization of the high-PT body-centered cubic (bcc) Fe under conditions of the Earth Inner Core  and how its stabilization interfere in the interpretation of iron melting curve and resolution of related enigmatic questions.
The mechanism of the high-PT bcc Fe phase stabilization is quite unique. The atoms in this structure move at times as in a liquid . Therefore, the mean square displacement never saturates and the diffusion coefficient and the viscosity of the bcc Fe are similar to those in very viscous liquid .
Recently, our theoretical prediction of the stability of high-PT bcc Fe phase [1,4] was confirmed by diamond anvil cell experiments . Interesting, that when a number of the experimental studies analyzed with the knowledge of the physics of the bcc Fe phase, those experiments confirm the stability of the new phase rather than contradict it.
I will show how the X-ray diffraction pattern of the bcc Fe looks like and discuss whether similar XRD patterns have already been observed in Fe high-PT melting experiments. I will demonstrate that the stabilization of the bcc phase was at times misinterpreted as melting.
The similarity of the bcc and liquid iron under extreme conditions of pressure and temperature revives the speculations on the existence of the critical solid-liquid point.
Acknowledgments: This work was supported by the Swedish Research Council.
 A. B. Belonoshko, T. Lukinov, J. Fu, J. Zhao, S. Davis, S. I. Simak Nature Geoscience 10, 312 (2017).
 A. B. Belonoshko, J. Fu, T. Bryk, S. I. Simak, M. Mattesini, Nature Communications 10, 1-7 (2019).
 A. B. Belonoshko, R. Ahuja, B. Johansson, Nature 424, 1032 (2003).
 R. Hrubiak, Y. Meng, G. Shen, arXiv:1804.05109 Experimental evidence of a body centered cubic iron at the Earth's core conditions.