condensed matter

Detection of 5/2 phases

Date: 
Thursday, July 7, 2022 - 10:30am to 12:00pm
Location: 
TBA
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Dr. Ankur Das

Postdoctoral Research Associate

Weizmann Institute of Science

Rehovot, Israel

 

Title: Detection of 5/2 phases

Abstract: The phases of the \nu=5/2 state have been shown to be very elusive but one of the most interesting ones as it is proposed to contain Majorana modes with non-abelian statistics. There is more than one candidate for the non-abelian state and among that three are the most promising ones namely pfaffian, anti-pfaffian, and particle-hole symmetric pfaffian. Quite a few experiments later the issue has not been settled. Previous efforts proposed methods to distinguish the candidates including the proposals where the order can be determined by measuring both thermal conductances and shot noise on the same device [Park et al. PRL 125, 157702 (2020)] or by only measuring the unequilibrated electrical conductance [Yutushui et al. PRL 128, 016401 (2022)]. To avoid some of the experimental challenges and limitations of the proposals including the above-mentioned ones we propose a new device made out of interfaces of the \nu=5/2 state and Abelian states. We propose to measure electrical shot noise to resolve among these states.

Superfluid Helium Electromechanics

Date: 
Tuesday, April 26, 2022 - 3:30pm to 5:00pm
Location: 
Zoom
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Professor John Davis

Associate Professor

University of Alberta

Department of Physics

 

Title:  Superfluid Helium Electromechanics

Abstract: Liquid helium posses many properties that make it an attractive medium for studies of mechanical systems in the quantum regime, such as low mechanical and dielectric losses.  The flip side of this is to imagine using optomechanics or electromechanics to revisit the novel physics of superfluid helium, including bosonic helium-4 and fermionic helium-3.  In particular, when spatially restricted in one dimension, helium superfluids are expected to demonstrate quasi-two dimensional behavior with qualitatively different physics than in three dimensions.  By using nanofabrication techniques to both confine the helium and provide an electromechanical detection scheme, we are beginning the journey of studying such two-dimensional superfluids.

TBA

Date: 
Tuesday, April 19, 2022 - 3:30pm to 5:00pm
Location: 
Blazer 339
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Dr. Allen Scheie

Postdoctoral Research Associate

Oak Ridge National Laboratory

Neutron Scattering Division

Title: Witnessing entanglement in quantum magnets using neutron scattering

Abstract: In this talk I show how information about solid state quantum entanglement can be extracted from magnetic neutron scattering using model-independent techniques. Using the 1D spin chain KCuF3, we examine three entanglement witnesses applicable to neutron scattering: one tangle, two tangle, and Quantum Fisher Information (QFI). We find that QFI is the most experimentally robust, giving good agreement between theory and experiment over all measured temperatures, and witnessing multipartite entanglement up to 75 K. We then apply the entanglement witnesses to the 2D triangular lattice KYbSe2, showing the presence of appreciable entanglement in the low temperature phase. We then use diffuse scattering fits, heat capacity comparisons, and nonlinear spin wave fits to demonstrate that KYbSe2 is proximate to a quantum spin liquid. We thus provide a rigorous route to studying and understanding highly entangled quantum phases.

Ultimate-density atomic semiconductor via flat phonon bands

Date: 
Tuesday, March 22, 2022 - 3:30pm to 5:00pm
Location: 
Blazer 335
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Professor Jun Hee Lee

School of Energy and Chemical Engineering

Ulsan National Institute of Science and Technology

South Korea

Title: Ultimate-density atomic semiconductor via flat phonon bands

Abstract: Dispersion-less flat energy bands in momentum space generate localized states and are known to cause unconventional phenomena such as graphene superconductivity in electrons and individual spin flips in magnons. However flat bands in phonon were not discovered yet. For the first time, we discovered flat bands in phonon exist surprisingly in a ferroelectric HfO2 and produce a localized motion of atoms as if their chemical bond temporarily disappears by an external voltage. With the vanishing bond, each atom can be freely displaced by the voltage for the information storage. Our discovery of the atom control directly in a solid will lead us to the design of ultimate-density memory semiconductors reaching up to ~100 TB [1]. Our theory is directly applicable to the Si-compatible HfO2 so can be materialized in all electronic devices [2]. Just as Einstein’s theory of relativity (E=mc2) enabled us to make bombs out of atoms not out of materials, with our “Atomic Semiconductor” we will open the era of designing memories on an atomic scale rather than a materials scale and carrying a data center in the palm of your hand.

 

[1] “Scale-free ferroelectricity driven by flat phonon bands in HfO2”, H.-J. Lee et al., Science 369, 1343 (2020).

 

[2] “A key piece of the ferroelectric hafnia”, B. Noheda et al., Science 369, 1300 (2020).

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.

Generalization of Bloch’s Theorem for Tight-binding Models: Quantum Dragon Nanomaterials and Nanodevices

Date: 
Tuesday, March 29, 2022 - 3:30pm to 5:00pm
Location: 
Blazer 335
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Professor Mark Novotny

Mississippi State University

Department of Physics and Astronomy

Title: Generalization of Bloch’s Theorem for Tight-binding Models:Quantum Dragon Nanomaterials and Nanodevices

Abstract: Bloch’s Theorem arguably has the largest economic impact of any condensed matter theorem.  Bloch’s Theorem can only be used for translationally invariant systems, and together with the tight-binding model gives band structures and hence devices such as transistors and optoelectronics.  For tight-binding models, a generalization of Bloch’s Theorem for some strongly disordered (non-translationally invariant) systems is stated and proved.  The theorem generalization leads to predictions of novel electrical properties for some nanomaterials and nanodevices with strong disorder, whimsically called quantum dragons [1].  A number of different predictions of quantum dragon materials and devices [2] will be presented.  Furthermore, conjectures and testing of scaling for materials that are ‘close to quantum dragons’ are given [3].  For example, a perfect quantum wire is one in which impinging electrons from an appropriate incoming lead have probability unity of propagating through the device to the end of an outgoing lead, T(E)=1, for all electron energies E that propagate through the leads. Some quantum dragons are predicted to be perfect quantum wires (see the device in the figure below [3]), while others may make a unique FET (Field Effect Transistor) or quantum sensor or spintronics nanodevice. 

[1] M.A. Novotny, Energy-independent total quantum transmission of electrons through nanodevices with correlated disorder, Phys. Rev. B 90, 165103 (2014).

[2] G. Inkoom and M. Novotny, Quantum dragon solutions for electron transport through nanostructures based on rectangular graphs, J. Physics Commun. 11, 115019 (2018). 

[3] M.A. Novotny and T. Novotný, Order amidst Disorder in 2D+3D Quantum Dragon Composite Nanodevices with varying Breadth, J. Phys: Conf. Ser. 1740, 012002 (2021).

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)

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