Condensed Matter Seminar
Fall 2023
Organizer: Yang Zhang [email protected]
Seminar Time: Wednesdays, 10:20-11:10 AM
Location: IAMM 147
Zoom for Virtual Seminars: https://tennessee.zoom.us/j/87862823041
August 23: Seminar Introduction on Zoom
Introduction to CAMM seminar and PHYS 599 https://tennessee.zoom.us/j/87862823041
August 30: Gia-Wei Chern (U Virginia), Hosted by C. Batista / Y. Zhang
Title: Machine Learning Force-Field Model for Dynamical Modeling of Correlated Electron Systems
Abstract: In this talk, I will present our recent efforts on using machine learning (ML) methods to enable multi-scale dynamical modeling of functional electron materials, and in particular correlated electron systems. I first discuss the ML force field models for large-scale dynamical simulations on two canonical examples of correlated electron systems: the double-exchange and the Falicov-Kimball models. The central idea is to develop deep-learning neural-network models that can efficiently and accurately predict generalized forces required for dynamical evolutions based on local environment. The large-scale simulations enabled by the ML method also reveal new phase-ordering dynamics in these correlated electron systems that is beyond conventional empirical theories. We will also discuss preliminary results of similar ML models for the more difficult Hubbard-type models. In the second part, generalization of the ML framework to represent nonconservative forces of out-of-equilibrium systems is discussed. In particular, we present a novel ML structure for modeling spin transfer torques that play a crucial role in spintronics.
September 06: Jason K Kawasaki (University of Wisconsin – Madison), Hosted by Joon Sue Lee
Title: Strain-Induced Magnetism and Superconductivity in Single-Crystalline Heusler Membranes
Abstract: Single-crystalline membranes of functional materials enable the tuning of properties via extreme strain states; however, conventional routes for producing membranes require the use of sacrificial layers and chemical etchants, which can both damage the membrane and limit the ability to make them ultrathin. I will describe how the growth of thin films on graphene-terminated substrates enables synthesis of single crystalline, mechanically exfoliatable membranes [1,2]. Using rippled membranes of the Heusler compound GdPtSb, we demonstrate the first experimental example of flexomagnetism, that is, ferro/ferri-magnetism induced by strain gradients [3]. I will also describe evidence of superconductivity induced in another Heusler membrane via strain. More broadly, Heusler membranes provide highly tunable platform for tuning ferroic order, topological states, and correlations [4].
- S. Manzo, et. al., Nature Commun., 13, 4014 (2022). https://doi.org/10.1038/s41467-022-31610-y
- D. Du et. al., Nano Lett. 22, 21, 8647 (2022). https://doi.org/10.1021/acs.nanolett.2c03187
- D. Du, et. al., Nature Commun., 12, 2494 (2021). https://doi.org/10.1038/s41467-021-22784-y
- D. Du, e. al. APL, 122, 170501 (2023). https://doi.org/10.1063/5.0146553
September 13: Chen Li (UC Riverside), Hosted by Y. Wang
Title: Scattering Studies of Lattice and Spin Dynamics
Abstract: Many scientific and technical challenges require materials with structural, electronic, magnetic, and transport properties tailored to specific applications. Knowledge of lattice and spin excitations in materials is critical to understanding these physical properties. Scattering tools are valuable for measuring the lattice and spin excitations in functional materials, including spintronic materials, thermoelectrics, negative thermal expansion materials, fast ion conductors, and low-dimension materials, under various environments. Exotic and novel physics often arises from the interplay between different degrees of freedom, such as phonon-phonon, electron-phonon, and magnon-phonon interactions. With the help of first-principles calculation, scattering simulation, and advanced data science tools, we use neutron and X-ray scattering to study these fundamental interactions to better understand existing materials and provide insights into the engineering of future materials.
September 20: Yi-Zhuang You (UCSD) on Zoom, Hosted by Y. Zhang
Title: Emergent Classicality from Information Bottleneck
Abstract: Our universe is quantum, but our everyday experience is classical. Where is the boundary between quantum and classical worlds? How does classical reality emerge in quantum many-body systems? Does the collapse of the quantum states involve intelligence? These are fundamental questions that have puzzled physicists and philosophers for centuries. The recent development of quantum information science and artificial intelligence offers new opportunities to investigate these old problems. In this talk, we present our preliminary research on using a transformer-based language model to process randomized measurement data collected from Schrödinger’s cat quantum state. We show that the classical reality emerges in the language model due to the information bottleneck: although our training data contains the full quantum information of Schrödinger’s cat, a weak language model can only learn the classical reality of the cat from the data. Our study opens up a new avenue for using the big data generated on noisy intermediate-scale quantum (NISQ) devices to train generative models for representation learning of quantum operators, which might be a step toward our ultimate goal of creating an artificial intelligence quantum physicist.
September 27: Markus Heyl (U Augsburg) on Zoom, Hosted by A. Tennant
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.
October 04: Fabian Heidrich-Meisner (University of Goettingen)
Title: Topological Charge Pumping with Ultracold Atomic Gases
Abstract: Clarifying the evolution of topological states of matter with interactions is a core goal of condensed matter theory, ranging from the stability of topological insulators to the emergent regime of topological quantum matter. Ultracold quantum gases in optical lattices provide unique opportunities to realize topological band structures, yet face challenges concerning the loading of the bulk and the stability against heating in the interacting case inherent to Floquet engineering scheme. Topological charge pumps are conceptionally related to integer quantum Hall effects via dimensional reduction, with a different physical manifestation via the quantized charge. Their realization, notably, does not require fast driving and relies on established experimental loading schemes and therefore, this system provides unique opportunities to investigate the effect of interactions. I will report on three main results. First, we investigated the stability of charge pumping in the bosonic systems. Second, we characterized the breakdown of quantized pumping due to the addition of quenched disorder. Finally, we turn to interacting fermions and show that interactions can change the pumped charge per cycle from the value obtained for noninteracting systems.
- A. Hayward, C. Schweizer, M. Lohse, M. Aidelsburger, and F. Heidrich- Meisner Phys. Rev. B 98, 245148 (2018)
- A. L. C. Hayward, E. Bertok, U. Schneider, and F. Heidrich-Meisner Phys. Rev. A 103, 043310 (2021)
- E. Bertok, F. Heidrich-Meisner, and A. A. Aligia Phys. Rev. B 106, 045141 (2022)
October 11: Di Luo (MIT), Hosted by Y. Zhang
Title: Infinite Neural Network Quantum States
Abstract: TBD
October 18: Ben Cohen-Stead (UTK), Hosted by S. Johnston
Title: Bond-Stretching Electron-Phonon Interactions in BaBiO3: a Hybrid Monte Carlo Study
Abstract: The relationship between electron–phonon (e-ph) interactions and charge-density-wave (CDW) order in the bismuthate family of high-temperature superconductors remains unresolved. We address this question using nonperturbative hybrid Monte Carlo calculations for the parent compound BaBiO3. Our model includes the Bi 6s and O 2p orbitals and coupling to the Bi-O bond-stretching branch of optical phonons via modulations of the Bi-O hopping integral. We simulate three-dimensional clusters of up to 4000 orbitals, with input model parameters taken from ab initio electronic structure calculations and a phonon energy of 60meV. Our results demonstrate that the coupling to the bond-stretching modes is sufficient to reproduce the CDW transition in this system, despite a relatively small dimensionless coupling. We also find that the transition deviates from the weak-coupling Peierls’ picture. This work demonstrates that off-diagonal e-ph interactions in orbital space are vital in establishing the bismuthate phase diagram.
October 25: Yuxuan Wang (UFL), Hosted by R. Zhang
Title: TBD
Abstract: TBD
November 01: Marek Kolmer (Ames National Lab), Hosted by Wonhee Ko
Topic: Manipulation of Atoms and Molecules with STM
Abstract: TBD
November 08: Haijing Zhang (Max Planck CPfS), Hosted by J. Liu
Title: Tuning Electronic Phase Transitions in Layered Quantum Materials
Abstract: The multifunctional behaviors of quantum materials are driven by the intricate interplay between charge, orbital and spin degrees of freedom. The quest to control the interplay of multiple degrees of freedom is indispensable in condensed matter physics, as it enables us to harness the multifunctionality of quantum devices on demand. In this talk, I will present how to employ an ionic gate to control the emerging physical phenomena in quantum devices, and how it offers new insights to the underlying physics. First, I will talk about the observation of a spontaneous anomalous Hall effect, a trademark of time-reversal symmetry breaking, in a layered polar semiconductor. Remarkably, the magnitude of anomalous Hall conductivity can be enhanced by tuning the carrier density, which sheds new light on the interplay of magnetic and ferroelectric-like responses [1]. Then, I will present some recent results on the electric field control at the interfaces of ionic gated tellurium thin flake devices. The Rashba spin-orbit coupling coefficient is demonstrated to increase fourfold.
References
[1] S. Kim et al. arXiv:2307.03541
November 15: Yuan Liu (NC State/MIT), Hosted by Y. Zhang
Title: New Quantum Algorithms for Old Challenges: from Quantum Simulation to Quantum Error Correction
Abstract: Harnessing the power of quantum computers and systems to solve important problems beyond the capability of classical computers is an outstanding challenge. In this talk, I will present our recent efforts on developing novel quantum algorithms to address longstanding challenges in quantum simulation, quantum error correction, and quantum chemistry. These progresses are made possible by leveraging the quantum embedding framework as well as a unified understanding for modern quantum algorithms via quantum signal processing. In addition to discrete-variable systems such as qubits, in the second part, I will present control protocols that exploit continuous-variable bosonic modes to perform universal qudit-based quantum computation. I will conclude the talk with a discussion on the prospects of using hybrid discrete-continuous-variable quantum systems for computation and information processing.
November 29: Bradraj Pandey (UTK), Hosted by Elbio Dagotto
Title: Mobile Majoranas in Chains and Y Geometries
Abstract: TBD