Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session T61: Precision Many Body Physics V: DynamicsFocus
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Sponsoring Units: DCOMP DAMOP DCMP Chair: Anouar Benali, Argonne National Laboratory Room: Room 418 |
Thursday, March 9, 2023 11:30AM - 12:06PM |
T61.00001: Dynamics of driven impurities in a quantum gas Invited Speaker: Meera Parish The problem of a quantum impurity in a Fermi gas is fundamental in physics, with relevance ranging from atomic gases to doped semiconductors to neutron stars. In this talk, I will discuss the behavior of impurities with internal spin states coupled by a continuous Rabi drive, a scenario that is readily realised in cold-atom experiments. I will show how this reveals quantum many-body phenomena such as the orthogonality catastrophe. |
Thursday, March 9, 2023 12:06PM - 12:18PM |
T61.00002: Quantum Monte Carlo for multi-orbital systems at steady-state Andre Erpenbeck, Thomas J Blommel, Wei-Ting Lin, Lei Zhang, Emanuel C Gull, Guy Cohen The description of nonequilibrium or real time dynamics in quantum impurity models with multiple interacting orbitals is challenging. In Monte Carlo methods based on hybridization expansions, this difficulty takes the form of a dynamical sign problem that exacerbates a multi-orbital sign problem already present in equilibrium calculations on the Matsubara contour. The result is a prohibitive computational cost that scales exponentially with both final simulation time and number of orbitals. We present a numerically exact Inchworm method for multi-orbital systems in the steady-state, where the inchworm expansion simultaneously alleviates both sign problems. The method extends our recently developed steady-state inchworm Monte Carlo framework [1] to multi-orbital systems. We demonstrate the performance of our method by comparison with analytical limits, and showcase its usage by considering the response of multi-orbital quantum dot systems to an external bias voltage in the strongly correlated regime. Our method can also be applied within quantum embedding schemes such as nonequilibrium DMFT. |
Thursday, March 9, 2023 12:18PM - 12:30PM |
T61.00003: Dynamical properties of the spin-boson model using real-time quantum Monte Carlo Olga Goulko, Guy Cohen, Moshe Goldstein, Hsing-Ta Chen The spin-boson model consists of a two-state system coupled to a bath of non-interacting harmonic modes. We obtain the real-time dynamics of the population difference between the two states using the inchworm Monte Carlo algorithm. We focus on sub-Ohmic spectral densities of the bosonic bath, where the system exhibits a second order quantum phase transition between localized and delocalized regimes, as well as a crossover between coherent and incoherent dynamics. The inchworm algorithm is efficient over a wide range of temperatures (including low, intermediate, and high temperatures) and thus allows us to examine the changes in dynamics as the temperature is increased above zero. We use this to study the quantum critical behavior at finite temperature and the emergence of a quantum critical fan. We also identify and analyze two competing mechanisms for the coherent-incoherent crossover and study their temperature-dependence. |
Thursday, March 9, 2023 12:30PM - 12:42PM |
T61.00004: Dynamic structure factor of spin-1/2 chains with long-range interactions Sibin Yang, Anders W Sandvik We study the dynamic structure factor of spin-1/2 chains with long-range power-law decaying unfrustrated interactions by means of stochastic analytic continuation (SAC) of quantum Monte Carlo (QMC) imaginary-time data. I will explain different parametrizations of the spectral function S(q,ω) in the SAC method and their applications in the antiferromagnetic (AFM) and quasi long-range ordered (QLRO) phases. The spectral functions are observed to evolve from one with a sharp quasi-particle peak (magnon) in the AFM phase to an edge with power-law divergent form in the QLRO phase as the exponent governing the power-law decay of the interactions is changed. This study can serve as a bench-mark for SAC/QMC studies of systems with a transition from conventional to fractionalized quasi-particles, which we also plan to study in 2D systems. |
Thursday, March 9, 2023 12:42PM - 12:54PM |
T61.00005: Extension of Dynamical Variational Monte Carlo and its application for Fermi arcs Peter Rosenberg, David Sénéchal, André-Marie S Tremblay, Maxime Charlebois The theoretical and numerical treatment of strongly-correlated many-electron systems requires the continued development of high-accuracy many-body approaches. One recently developed method is dynamical Variational Monte Carlo (dVMC) [1], which enables the computation of the Green's function for large systems. In this work [2] we present a generalized dVMC technique that can serve as an impurity solver in quantum cluster methods. Using this new approach we perform a systematic study of the doped t-t'-t'' Hubbard model using cluster perturbation theory with a dVMC impurity solver. We reach system sizes unattainable by exact diagonalization solvers, and find robust evidence of the existence of Fermi arcs, a result of direct relevance to the cuprate superconductors. |
Thursday, March 9, 2023 12:54PM - 1:06PM |
T61.00006: Energies and spectra of correlated metals via the algorithmic inversion of dynamical potentials Tommaso Chiarotti, Andrea Ferretti, Nicola Marzari Dynamical (frequency-dependent) potentials are needed to predict accurate spectral properties, and arise in embedding theories. The frequency dependence transforms the problem from the diagonalization of an operator (e.g., the Kohn-Sham Hamiltonian of density-functional theory) to the Dyson inversion of a self-energy. Here, we propose a novel treatment of dynamical potentials able to solve Dyson-like equations via an exact mapping to an effective non-interacting problem. The sum-over-poles representation of the self-energy, together with the static contribution to the Hamiltonian, are used to build a (larger) effective Hamiltonian that has the excitation energies of the system as eigenvalues and the Dyson orbitals as a projection of the eigenvectors. The Green's function of the system is also obtained as a sum over poles, and allows for the computation of both spectral and thermodynamic properties. To explore applications on real materials, we introduce a localized-GW Klein functional exploiting the frequency-resolved screened-potential U(ω), and we apply it to calculate the spectral and mechanical properties of SrVO3. |
Thursday, March 9, 2023 1:06PM - 1:18PM |
T61.00007: Dynamic response of the homogeneous electron gas Igor Tupitsyn, James LeBlanc, Kun Chen, Kristjan Haule, Nikolay Prokof'ev To predict functional behavior of new materials, the knowledge of their dynamic response functions at finite temperature is of fundamental importance. In this context, the homogeneous electron gas (jellium) model plays a special role both as a paradigmatic system for understanding the physics of the electron liquid in solids as well as being the key element in the formulation of the time-dependent density functional theory (TDDFT). Here we introduce a diagrammatic Monte Carlo technique based on algorithmic Matsubara integration that allows us to compute frequency and momentum resolved finite temperature responses directly in the real frequency domain using series of connected Feynman diagrams. Using the obtained data for charge response at moderate electron density we for the first time computed the exchange-correlation kernel for jellium by a controlled method and revealed unexpected features in its frequency dependence, which should spark the development of better kernels for TDDFT both at zero and finite temperature. |
Thursday, March 9, 2023 1:18PM - 1:30PM |
T61.00008: Effect of quasiparticle self-consistent schemes on the GW method with Bloch Gaussian orbitals Gaurav Harsha, Vibin Abraham, Ming Wen, Dominika Zgid The GW method is one of the simplest, yet non-trivial, approximations to the self-energy of a many-electron system, which has been shown to be successfull on a wide variety of systems. For example, it can accurately predict the band gaps of many weakly correlated systems (solids and molecules) and is often chosen as the low-level theory for more sophisticiated embedding methods such as the dynamical mean-field theory, or the self-energy embedding theory. However, the result in a GW calculation can be very sensitive to the choice of basis set, whether or not relativistic effects are to be considered, as well as the type of self-consistency or quasiparticle approximations that are used (or if they are used). In this talk, we will compare band-gaps for insulators and semi-conductors using various self- consistent quasiparticle GW schemes against the one-shot G0W0 and fully self-consistent results. Interestingly, we find that the trends in the accuracy of the quasiparticle schemes that have been observed in previous studies (using plane waves or linear augmented plane wave basis sets) does not necessary translate to Gaussian orbitals. We will also touch upon the effect of other factors, such as relativity, temperature, etc., on these findings. |
Thursday, March 9, 2023 1:30PM - 1:42PM |
T61.00009: Theoretical simulation of molecular valence and core photoemission spectra with GW approaches Ming Wen, Vibin Abraham, Gaurav Harsha, Dominika Zgid The GW methodology provides an explicit interpretation of charged excited states in chemical system. As a result, it has been used extensively to investigate theoretical spectroscopy of both periodic crystalline structure and small molecules. Here we present our finite temperature GW methods with different levels of consistency (for example, scGW and G0W0), which provides accurate estimation of valence electron photoexcitation spectra for molecules. We compare the results with both experimental energies and CCSD(T) references. In addition to the well-benchmarked test of valence excitation on the GW100 set, we also demonstrate that our GW schemes can be used to render inner shell photoemission spectra using accurate analytical continuation. Additional entries involving transitional metals were included to the GW100 subset for core level spectra. We also examine how the GW results compare with Delta methods (ΔHF and ΔCC). |
Thursday, March 9, 2023 1:42PM - 1:54PM |
T61.00010: Phonon Modulated Hopping Polarons: X-representation Technique Boris Svistunov, Nikolay Prokof'ev We report a breakthrough development allowing one to solve a broad class of polaron problems with highly nonlinear electron-phonon coupling that were considered unsolvable without uncontrolled simplifications in the past using a Monte Carlo technique formulated in the coordinate representation for both the particle and the atomic displacements. The only condition is the sign positivity of the hopping amplitude. The technique dramatically simplifies (with the corresponding efficiency gains) for models with dispersionless phonons. Our study sheds important light on the nature and universality of the most striking qualitative and quantitative effects demonstrated by the "standard" (Peierls/Su-Schrieffer-Heeger) model based on the linearized displacement-modulated hopping. |
Thursday, March 9, 2023 1:54PM - 2:06PM |
T61.00011: Emergence of geometry-driven topological defects in two-dimensional effectively hyperuniform systems Sungyeon Hong, Nicolas Francois, Mohammad Saadatfar Hyperuniform structures are characterised by an unusual suppression of large-scale density fluctuations of their constitutive units. These structures have been observed in a diverse range of systems, leading to distinctive physical properties differing from their crystalline counterparts, and there is a growing interest in finding design paths to produce them. A recent study showed that initially random point patterns can evolve into effectively hyperuniform configurations (EHU) under an iterative geometric process, known as the Lloyd’s algorithm (Klatt et al. 2019). |
Thursday, March 9, 2023 2:06PM - 2:18PM |
T61.00012: Quantum nonequilibrium dynamics from Knizhnik-Zamolodchikov equations Tigran A Sedrakyan, Hrachya M Babujian In this talk, we will discuss a set of non-stationary quantum models. We show that their dynamics can be studied using links to Knizhnik-Zamolodchikov (KZ) equations for correlation functions in conformal field theories. We specifically consider the boundary Wess-Zumino- Novikov-Witten model, where equations for correlators of primary fields are defined by an extension of KZ equations and explore the links to dynamical systems. As an example of the workability of the proposed method, we provide an exact solution to a dynamical system that is a specific multi-level generalization of the two-level Landau-Zenner system known in the literature as the Demkov-Osherov model. The method can be used to study the nonequilibrium dynamics in various multi-level systems from the solution of the corresponding KZ equations. |
Thursday, March 9, 2023 2:18PM - 2:30PM |
T61.00013: Photoinduced structural dynamics across metal-insulator transition in nickelate thin films Jugal Mehta, Scott Smith, Jianheng Li, Rahul Jangid, Kenneth Ainslie, Nadia Albayati, Pooja Rao, Yu-Hsing Cheng, Spencer Jeppson, Donald A Walko, Haidan Wen, David Lederman, Roopali Kukreja Rare earth nickelates display metal-insulator transition (MIT) which is accompanied by a magnetic transition, charge ordering, and a crystal structure change from orthorhombic to monoclinic. The size of the rare-earth cation affects the onset of MIT and the magnetic transition. Laser-induced excitation drives the transition at ultrafast timescales and can be used in combination with time resolved x-ray diffraction to disentangle the contribution of competing degrees of freedom. In this study, we focused on measuring the laser fluence dependent photoinduced structural response of epitaxial NdNiO3/ SrTiO3 (NNO/STO) and SmNiO3/SrTiO3 (SNO/STO) thin films. We utilized time-resolved x-ray diffraction to observe the evolution of the out of plane (002)pc Bragg peak and the in-plane (1-13)/2pc Bragg peak of NNO and SNO after laser excitation. The out of plane lattice parameter of NNO contracts for low fluences and expands for high fluences after laser excitation whereas an expansion in the SNO out of plane lattice parameter is observed for all fluences. The significantly faster structural recovery timescales of NNO compared to SNO indicate the role of the initial magnetic state on the photoinduced process. |
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