Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M46: Excited State III: electron-phonon couplingFocus Recordings Available
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Sponsoring Units: DCOMP DMP Chair: Feliciano Giustino, University of Texas Room: McCormick Place W-470A |
Wednesday, March 16, 2022 8:00AM - 8:36AM |
M46.00001: Electron-Vibrational Coupling in and beyond The Phonon Picture: Concepts and Applications to Thermal and Electrical Conductivity Invited Speaker: Matthias Scheffler Strong anharmonicity and its critical effect on materials properties are more frequent than typically presumed. In fact, for many materials and realistic temperatures, the observed structure and symmetry is a statistical average of energetically degenerate, lower-symmetry geometries. Here phonon-based perturbation theories break down, and an explicit treatment of the nuclear dynamics in terms of ab initio molecular dynamics becomes necessary to account for such strong anharmonic effects. |
Wednesday, March 16, 2022 8:36AM - 8:48AM |
M46.00002: Time-dependent GW approach with finite-momentum electron and phonon couplings Zhenglu Li, Yang-hao Chan, Steven G Louie In recent years, ultrafast and pump-probe experiments have significantly advanced the studies of nonequilibrium charge and exciton dynamics in molecules, bulk solids, and reduced-dimensional materials. The ab initio time-dependent GW approach, as a nonequilibrium generalization of the conventional GW and GW plus Bethe-Salpeter equation approaches for equilibrium properties, has developed rapidly. Existing methods are usually based on the adiabatic approximation to the self-energy and contain only zero momentum transfer interaction processes. In reality, finite momentum couplings are found critical to dynamical processes (e.g., intervalley coupling in 2D transition metal dichalcogenides). Here, we present progress on including finite-momentum transfers from electron-electron, electron-hole, and electron-phonon interactions in the time-dependent adiabatic GW approach. We discuss the generalized formalism, its practical implementations and algorithms, as well as some results. |
Wednesday, March 16, 2022 8:48AM - 9:00AM |
M46.00003: Ab initio Green's function theory of polarons Jon Lafuente-Bartolome, Idoia G Gurtubay, Asier Eiguren, Feliciano Giustino State-of-the-art ab initio approaches to study polarons fall into two main categories: many-body perturbation theory methods and adiabatic DFT calculations. In this talk, we present a general Green's function theory of self-trapped polarons which unifies these two seemingly disconnected approaches. We outline a series of approximations that make our theory readily amenable for implementation in current codes, and provide benchmark calculations within the Fröhlich model. This work opens the way towards full many-body calculations of polarons in real materials. |
Wednesday, March 16, 2022 9:00AM - 9:12AM |
M46.00004: Many-body Green's function analysis of the doped Fröhlich solid Nikolaus M Kandolf, Carla Verdi, Feliciano Giustino In polar semiconductors and insulators, the Fröhlich interaction between electrons and long- wavelength longitudinal optical phonons induces a many-body renormalization of the carrier effective masses and the appearance of characteristic 'polaron satellites' in the spectral function. The simplest and most widely used model that captures these effects is the Fröhlich model, which focuses on undoped systems and ignores carrier screening and Pauli blocking effects that are present in real experiments on doped samples. To overcome this limitation, we have extended the Fröhlich model to the case of doped solids, allowing us to provide exact solutions for the electron spectral function, mass enhancement, and polaron satellites. In our analysis we compare two approaches, namely Dyson's equation with the Fan-Migdal self-energy, and the second order cumulant expansion. |
Wednesday, March 16, 2022 9:12AM - 9:24AM |
M46.00005: Phonon-assisted luminescence in qubits from many-body perturbation theory Francesco Libbi, Pedro M Melo, Zeila Zanolli, Matthieu J Verstraete, Nicola Marzari Phonon-assisted luminescence is a key property of defect centers in semiconductors, and can be measured to perform the readout of the information stored in a quantum bit, or to detect temperature variations. The investigation of phonon-assisted luminescence usually employs phenomenological models, such as that of Huang and Rhys, with restrictive assumptions that can fail to be predictive. In this work, we predict luminescence and study exciton-phonon couplings within a rigorous many-body perturbation theory framework, an analyisis that has never beenperformed for defect centers. In particular, we study the optical emission of the negatively-charged boron vacancy in 2D hexagonal boron nitride, which currently stands out among defect centers in 2D materials thanks to its promise for applications in quantum information and quantum sensing. We show that phonons are responsible for the observed luminescence, which otherwise would bedark due to symmetry. We also show that the symmetry breaking induced by the static Jahn-Teller effect is not able to describe the presence of the experimentally observed peak at 1.5 eV. |
Wednesday, March 16, 2022 9:24AM - 9:36AM |
M46.00006: Gaining an Atomistic Understanding of Auger Recombination in Crystalline Silicon Kyle M Bushick, Emmanouil Kioupakis Auger recombination is an intrinsic, non-radiative recombination mechanism involving three carriers – either two electrons and a hole (eeh) or two holes and an electron (hhe). Despite silicon's overwhelming importance as a semiconductor, the microscopic mechanisms of Auger recombination in silicon remain poorly understood. In this work, we use first principles methods to probe both direct Auger, where momentum is strictly conserved by the recombining electrons and holes, as well as indirect (phonon-assisted) Auger, which is enabled by the additional momentum provided via electron-phonon coupling. We demonstrate that phonon-assisted Auger is the dominant mechanism for both the eeh and hhe processes. Our results are in excellent agreement with experimental measurements. Furthermore, our analysis reveals that it may be possible to tune the Auger recombination rate in silicon via strain engineering. Ultimately, our work paves the way for a clearer understanding of this important recombination mechanism in silicon, and points to engineering solutions that may improve the efficiency of silicon devices such as solar cells. |
Wednesday, March 16, 2022 9:36AM - 9:48AM |
M46.00007: First-principles study of lattice and magnetic temperature effects on the optical properties of ferromagnetic BCC Fe Kisung Kang, Andre Schleife, David G Cahill Pump-probe magneto-optical spectrum measurements of magnetic materials have been utilized to investigate the (de)magnetization process and spin dynamics via the temperature-dependent optical response. First-principles density functional theory has successfully predicted the frequency-dependent dielectric function at 0K and recently studied the introduction of the lattice temperature using phonon dispersion. In this work, we develop an analogous approach based on atomistic spin dynamics to compute optical spectra at finite magnetic temperatures. We found that the imaginary part of the averaged diagonal component of optical conductivity at a low photon energy range grows drastically as both lattice and spin temperatures increase, which is induced by a huge change in matrix elements of low-energy optical transitions. A peak near 3 eV in the imaginary part of diagonal optical conductivity redshifts as the lattice and spin temperatures rise, explaining the discrepancy of the peak position between 0 K and measurement at 300 K. Spin temperature induced shifts contribute about four times more than shifts due to lattice temperature. Based on the result, this work might be expanded to the optical properties calculation of paramagnets or antiferromagnets. |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M46.00008: Novel First-Principles Tools for Electron Dynamics in Quantum Materials and Devices Marco Bernardi Understanding electron dynamics in quantum materials and devices presents new challenges and opportunities. In this talk, I will discuss novel first-principles tools developed in my group to study transport in electric and magnetic fields in quantum materials with spin-orbit coupling, nontrivial band topology, and strong electronic correlations. Methods to accurately predict spin relaxation and defect-mediated scattering, of relevance for quantum devices, will also be discussed. I will conclude by highlighting progress on our open-source code, PERTURBO, to make these new computational methods and workflows available to the community. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M46.00009: Ab initio electron dynamics in high electric fields: accurate predictions of velocity-field curves Ivan Maliyov, Jinsoo Park, Marco Bernardi Electron dynamics in external electric fields governs the behavior of solid-state electronic devices. First-principles calculations enable precise predictions of charge transport in low electric fields. However, studies of high-field electron dynamics remain challenging due to a lack of accurate and broadly applicable methods. Here we develop an efficient approach to solve the Boltzmann transport equation in the time domain with both the electric field advection term and ab initio electron-phonon collisions. These simulations provide field-dependent electronic distributions with a femtosecond resolution, allowing us to investigate both ultrafast and steady-state carrier dynamics in electric fields ranging from low to high (>10 kV/cm). The broad capabilities of our approach are demonstrated by computing time-dependent electron occupations and the drift velocity vs. electric field curves in Si, GaAs, and graphene. Our approach allows us to investigate microscopic details of transport in high electric fields, including the dominant electron-phonon scattering mechanisms and valley occupation dynamics. Our work provides a timely, robust, parameter-free method to compute high-field electrical transport, which will be instrumental in advancing the discovery and design of novel electronic materials. |
Wednesday, March 16, 2022 10:12AM - 10:24AM |
M46.00010: Ultrafast dynamics of hot carriers in bulk semiconductors and in accumulation layer: energy transfer and screening effects. Jelena Sjakste Electron-phonon coupling determines the charge transport properties in pure materials as well as the relaxation dynamics of photoexcited carriers. A computational method based on density functional theory (DFT) and on interpolation of the electron-phonon matrix elements in Wannier space allowed to successfully interpret the dynamics of photoexcited electron relaxation in several semiconductors, such as GaAs, Si, InSe, in good agreement with two-photon photoemission experiments. |
Wednesday, March 16, 2022 10:24AM - 10:36AM |
M46.00011: Towards mixed quantum-classical simulations of nonequilibrium phenomena in bulk and low-dimensional materials Roel Tempelaar, Alex Krotz, Justin Provazza The recent years have seen an increased interest in crystalline materials featuring strong coupling of electronic carriers to lattice vibrations, including monolayer transition-metal dichalcogenides. Strong electron-vibrational coupling has been well studied in molecular assemblies, where mixed quantum-classical dynamics (MQCD) has emerged as a prominent simulation tool. The equations of motion involved in MQCD are traditionally solved in real space, which is appropriate for molecules where excitations are localized and amenable to real-space truncations. For crystals with band-like properties, however, excitations are delocalized over large spatial domains. I will present our recent efforts aimed at reformulating MQCD within a reciprocal-space representation tailored to describing delocalized, Bloch-like excitations. Since such excitations tend to "localize" within the Brillouin zone (BZ), computations can be kept feasible by truncating the transformed electronic and vibrational bases to the BZ regions of interest. Results will be presented for both mean-field MQCD and surface hopping. The latter is shown to yield accurate short- and long-time behavior, offering exciting prospects for the simulation of nonequilibrium phenomena in bulk and low-dimensional materials. |
Wednesday, March 16, 2022 10:36AM - 10:48AM |
M46.00012: First-principles calculations of electron-phonon interactions with GW corrections for localized defect states in monolayer WS2 with a sulfur vacancy Jun-Ho Lee, Jonah B Haber, Jeffrey B Neaton Recent scanning tunneling spectroscopy measurements on a sulfur vacancy (VS) in monolayer WS2 have observed that in-gap defect states feature prominent sideband structure, a signature of strong electron-phonon (el-ph) interactions. Here, we use a combination of density functional theory (DFT) and ab initio many-body perturbation theory within the GW approximation to calculate defect states associated with VS in monolayer WS2 and their el-ph interactions. For each vibrational state, we compute Huang-Rhys factors via first-principles including spin-orbit coupling (SOC) in a fully relativistic way. We find that just a few specific phonon modes couple strongly with the defect levels and that two defect levels split by SOC couple to the same modes, but different strengths. We also find that inclusion of exact exchange and electron-electron correlations using the GW method substantially renormalizes the coupling strength in a mode-dependent fashion, giving rise to better agreement with experimental spectral lineshapes. This work enables a deeper understanding of el-ph interactions in systems that feature localized electronic states and provides a route for predicting spectral features associated with defects with higher accuracy using first-principles calculations. |
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