Condensed Matter Seminar
Spring 2024
Organizer: Ruixing Zhang [email protected]
Seminar Time: Wednesdays, 10:20-11:10 AM
Location: IAMM 310 or 147
Zoom for Virtual Seminars: https://tennessee.zoom.us/j/81386068237
January 31: Gabor Halasz (Quantum Science Center, ORNL) host Alan Tennant
Location: IAMM 310
Title: Thermal Anyon Interferometry in Phonon-Coupled Kitaev Spin Liquids
Abstract: Recent theoretical studies inspired by experiments on the Kitaev magnet α-RuCl3 highlight the nontrivial impact of phonons on the thermal Hall conductivity of chiral topological phases. We introduce mixed mesoscopic-macroscopic devices that allow refined thermal-transport probes of non-Abelian spin liquids with Ising topological order. These devices feature a quantum-coherent region with quantized or negligible phonon conductance, flanked by macroscopic lobes that facilitate efficient thermalization between chiral Majorana edge modes and bulk phonons. We show that our devices enable (i) accurate determination of the quantized thermal Hall conductivity, (ii) identification of non-Abelian Ising anyons via the temperature dependence of the thermal conductance, and, most interestingly, (iii) single-anyon detection through heat-based anyon interferometry. Analogous results apply broadly to phonon-coupled chiral topological orders.
February 7: Yuxuan Wang (University of Florida) host Ruixing Zhang
Location: IAMM 310
Title: Gapless Fermionic Systems as Phase-space Topological Insulators: Non-perturbative Results from Anomalies
Abstract: We present a theory unifying the topological responses and anomalies of various gapless fermion systems exhibiting Fermi surfaces, including those with Berry phases, and nodal structures, which applies beyond non-interacting limit. As our key finding, we obtain a general approach to directly relate gapless fermions and topological insulators in phase space, including first- and higher-order insulators. Using this relation we show that the low-energy properties and response theories for gapless fermionic systems can be directly obtained without resorting to microscopic details. Our results provide a unified framework for describing such systems using well-developed theories from the study of topological phases of matter.
Reference: Taylor Hughes and Yuxuan Wang, arXiv:2401.08744.
February 14: Markus Heyl (University of Augsburg) host Alan Tennant
Location: Virtual seminar (https://tennessee.zoom.us/j/81386068237)
Title: Solving 2D Quantum Matter with Neural Quantum States
Abstract: Accessing theoretically the ground state of interacting quantum matter has remained a notorious challenge especially for complex two-dimensional systems. Recent developments have highlighted the potential of neural quantum states to solve the quantum many-body problem by encoding the quantum many-body wave function into artificial neural networks. So far, however, this method faces the critical limitation that the training of modern large-scale deep network architectures has not yet been possible, thereby failing to capitalize on the full power of artificial neural networks. Here, we introduce an optimization algorithm for neural quantum states, which allows to train unparalleled deep artificial neural networks yielding unprecedented accuracies for the ground states of large complex two-dimensional quantum spin models. We demonstrate the power of the formulated minimum-step stochastic reconfiguration (MinSR) method for the paradigmatic spin-1/2 Heisenberg J_1-J_2 models on the square lattice, yielding significantly better variational energies as compared to existing numerical results approaching different levels of machine precision on modern GPU and TPU hardware. We expect that the MinSR method provides the tool to solve the quantum many-body problem by means of deep neural quantum states on a new level with potential applications not only in quantum many-body physics but also condensed matter and quantum chemistry.
February 21: Adrian Feiguin (Northeastern University) host Steve Johnston
Location:TBA
Title: TBA
Abstract: Forthcoming
February 28: Shi-Zeng Lin (Los Alamos National Lab) host Yang Zhang
Location:TBA
Title: Theory of Giant Phonon Magnetic Moment in Doped Dirac Semimetals
Abstract: Generally, the phonon magnetic moment is believed to be small compared to the electron’s magnetic moment due to the large ion mass. However, several recent experiments have observed large phonon magnetic moments that are comparable to the electron magnetic moment in many materials, including band insulators, topological insulators, and Dirac semimetals. In this talk, I will present a new theoretical framework to calculate the phonon magnetic moment in doped Dirac semimetals, motivated by the recent experimental observation of giant phonon magnetic moment in these materials. Our theory is based on the emergent gauge approach, which can handle both insulators and semimetals, unlike previous theories that are only applicable to insulators. I will show that the phonon magnetic moment is linked to the Hall conductivity through the phonon Hall viscosity. I will apply our theory to 2D and 3D Dirac semimetals, such as graphene and Cd3As2, and obtain large phonon magnetic moments of the order of the electron Bohr magneton using electron-phonon couplings from first-principle calculations. I will also discuss the conditions for employing the emergent gauge approach. Our theory not only explains the recent experimental findings but also provides practical guidance for the dynamic generation of large magnetization in materials.
March 19: Fang Chen (Chinese Academy of Science) host Jian Liu
Location:TBA
Title: TBA
Abstract: Forthcoming
March 20: William Faugno (Tohoku University) host Ruixing Zhang
Location:TBA
Title: TBA
Abstract: Forthcoming
March 27: Binghai Yan (Weizmann Institute of Science) host Ruixing Zhang
Location:TBA
Title: TBA
Abstract: Forthcoming
April 3: Mark Dean (Brookhaven National Lab) host Steve Johnston
Location:TBA
Title: TBA
Abstract: Forthcoming
April 10: Stefano Marchesini (SLAC) host Norman Mannella
Location:TBA
Title: TBA
Abstract: Forthcoming
April 17: Brian S.Y. Kim (University of Arizona) host Wonhee Ko
Location:TBA
Title: TBA
Abstract: Forthcoming
April 24: Ehsan Khatami (San Jose State University) host Steve Johnston
Location:TBA
Title: TBA
Abstract: Forthcoming
May 1: Zhen Bi (Penn State) host Ruixing Zhang
Location:TBA
Title: TBA
Abstract: Forthcoming
May 8: Mingda Li (MIT) host Yishu Wang
Location:TBA
Title: TBA
Abstract: Forthcoming