condensed matter

TBA

Date: 
Thursday, October 21, 2021 - 3:30pm to 4:30pm
Location: 
Zoom
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Dima Pesin

Associate Professor of Physics

University of Virginia

Title: TBA

Abstract: TBA

Photophysics of organic materials: from ancient pigments to high-performance organic semiconductors

Date: 
Tuesday, October 5, 2021 - 3:30pm to 5:00pm
Location: 
Zoom
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Oksana Ostroverkhova

Professor of Physics

Oregon State University

Title: Photophysics of organic materials: from ancient pigments to high-performance organic semiconductors

 

Abstract: Organic (opto)electronic materials have been explored in a variety of applications in electronics and photonics. They offer several advantages over traditional silicon technology, including low-cost processing, fabrication of large-area flexible devices, and widely tunable properties through functionalization of the molecules. Over the past decade, remarkable progress in the material design has been made, which led to a considerable boost in performance of organic thin-film transistors, solar cells, and other applications that rely on photophysics and/or (photo)conductive properties of the material. Nevertheless, a number of fundamental questions pertaining to light-matter interactions and charge carrier photogeneration and transport in these materials remain. In this presentation, I will give examples of our efforts aiming to understand and tune exciton, polariton, and charge carrier dynamics in high-performance organic materials and to develop novel, sustainable organic materials.

Coulomb Universe in a Jellium Droplet

Date: 
Wednesday, September 22, 2021 - 4:00pm to 5:30pm
Location: 
Blazer 339
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Special Joint Semiar with Astronomy

Eugene Kolomeisky

Associate Professor of Physics

University of Virginia

Title: Coulomb Universe in a Jellium Droplet

Abstract: Analogy between the Coulomb law of interaction between charges and the Newton law of gravitational attraction between masses is familiar to every physics student.  In this talk I demonstrate that this analogy implies that a system of identical charges can evolve with time in a manner that parallels cosmological evolution of the physical Universe with hallmarks such as Hubble's law and Friedmann-type dynamics present.  The Coulomb and Newton laws are also dissimilar because the electrostatic force is many orders of magnitude larger than the gravitational force whose manifestations are only noticeable on astronomical scale.  On the other hand, analog cosmological evolutions driven by Coulomb interactions are predicted to be observable in laboratory experiments involving Coulomb explosions and electron density oscillations in conductors.

 

Correlated and Topological Phases in flat bands of two-dimensional crystals

Date: 
Tuesday, September 14, 2021 - 3:30pm to 5:00pm
Location: 
Zoom
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Yafis Barlas

Assistant Professor of Physics

University of Nevada, Reno

Title: Correlated and Topological Phases in flat bands of two-dimensional crystals

Abstract: Due to their vanishing density of states and gapless semi-metallic behavior at charge neutrality, honeycomb lattice two-dimensional (2D) crystals are ideal candidates to host topological states. Even more interesting are twisted or strained 2D crystals, as the electron dispersion in these systems can be weakly dispersing, (i.e exhibit a small bandwidth) or completely flat. In these situations, the interplay of topology and correlation driven phases in flat bands of 2D crystals can result in emergent topological order.  Similarly, at high magnetic fields, multi-layer graphene and twisted bilayer graphene exhibit topological bands and various correlated states. In this talk, I will discuss a new class of interacting and non-interacting symmetry protected topological phases stabilized by mirror symmetry in 2D Dirac semi-metals. This quantum parity Hall state, exhibits two one-dimensional counter-propagating metallic edge states, distinguished by even or odd parity under the system’s mirror reflection symmetry.​ I will also discuss some of our results in twisted 2D crystals at high magnetic fields.

TBA

Date: 
Tuesday, March 29, 2022 - 3:30pm to 5:00pm
Location: 
TBA
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Professor Mark Novotny

Mississippi State University

Department of Physics and Astronomy

Title: TBA

Abstract: TBA

Complex geometrical phases in quantum materials probed by transport

Date: 
Tuesday, April 20, 2021 - 3:30pm to 5:00pm
Location: 
Zoom
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Professor Hiro Nakamura

Department of Physics

University of Arkansas

Host: Seo

Title: Complex geometrical phases in quantum materials probed by transport

Abstract: Recent advances in condensed matter physics brought the phase part of wavefunction in the forefront, as exemplified by the Berry phase in graphene. However, experimentally probing complex phases in a momentum space is not easy. In this talk, we present how advanced transport techniques such as quantum interference and planer Hall effect could shed light on higher-order and/or anisotropic quantum phases in solids. We show recent application of these techniques to three-dimensional (3D) topological antiperovskites, which points to a unique spin/pseudospin texture in this material [1,2]. Preliminary results from a 2D material with distinct spin texture (few-layer WSe2) also showcase an impact of different anisotropy of such phase patterns.

1. H. Nakamura et al., Nature Comm. 11, 1161 (2020).
2. D. Huang, H. Nakamura, and H. Takagi, arXiv:2101.05512 (2021)

Condensed Matter Seminar: Magnetic excitations in honeycomb and pyrochlore iridates with strong spin-orbit coupling and electron correlation

Date: 
Tuesday, April 25, 2017 - 3:30pm to 4:30pm
Location: 
CP 111
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Recent discovery of topological electronic states has shed light on the role of strong spin-orbit coupling in condensed mater. When the coupling is combined with electron correlation effect, their combination leads to a new class of topological states accompanying exotic magnetism. The 5d transition metal iridates have received considerable attention as the candidates that harness Kitaev quantum spin liquid, Wyle semimetal or Axion insulator phases. For the first part of this talk, I discuss resonant inelastic x-ray scattering (RIXS) investigation of a honeycomb Na2IrO3. The observation of diffuse magnetic scattering points to presence of short-range magnetic orders resulting from competition of bond-directional magnetic anisotropies. This validates the novel route to realize Kitaev spin liquid and evidences the proximity to the spin liquid phase. In the second part, I present RIXS study of magnetic excitation in a pyrochlore Eu2Ir2O7. Its metal-insulator transition driven by all-in-all-out (AIAO) magnetic order is regarded as possible realization of topological Weyl semimetal. We observe gradual softening of the magnon excitations in the entire Brillouin zone while warming, whose temperature evolution shows a direct relationship with the metal-insulator transition. This result suggests substantial change of magnetic exchange due to the varying electronic structure, and thereby classifies intermediate electron correlation strength: a requisite for realizing Weyl semimetal state.

Condensed Matter Seminar: Skyrmion charge, non-commutative momenta, and Hall transport"

Date: 
Tuesday, October 27, 2015 - 4:00pm to 5:00pm
Location: 
CP179
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Fermion space charge in narrow-band gap semiconductors, Weyl semimetals and around highly charged nuclei

Date: 
Tuesday, September 15, 2015 - 3:30pm to 4:30pm
Location: 
CP179
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The field of charged impurities in narrow-band gap semiconductors and Weyl semimetals can create electron-hole pairs when the total charge Ze of the impurity exceeds a value Z_{c}e.  Particles of one charge escape to infinity, leaving a screening space charge.  The result is that the observable dimensionless impurity charge Q_{infinity} is less than Z but greater than Z_{c}.  There is a corresponding effect for nuclei with Z >Z_{c} \approx 170, however in the condensed matter setting we find Z_{c} to be about 10.  Thomas-Fermi theory indicates that Q_{\infinity} = 0 for the Weyl semimetal, but we argue that this is a defect of the theory. For the case of a highly-charged recombination center in a narrow band-gap semiconductor (or of a supercharged nucleus),  the observable charge takes on a nearly universal value.  In Weyl semimetals the observable charge takes on the universal value Q_{infinity} = Z_{c} set by the reciprocal of material's fine structure constant.

Special Condensed Matter Seminar: Gravitational Response in Topological Insulators

Date: 
Tuesday, November 25, 2014 - 1:00pm to 2:00pm
Location: 
CP179
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