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 D59: First-Principles Simulations of Excited-State Phenomena: Electron-Phonon Interactions IFocus
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Sponsoring Units: DCOMP Chair: Sohrab Ismail-Beigi, Yale University Room: Room 301 |
Monday, March 6, 2023 3:00PM - 3:36PM |
D59.00001: Phonon-mediated quantum processes in semiconductors from first principles Invited Speaker: Emmanouil Kioupakis Quantum processes among electrons, excitons, photons, and phonons lie at the heart of the operation of semiconducting devices for electronics, optoelectronics, and energy applications. Many of these processes are direct, such as the absorption and emission of light in direct-gap semiconductors, and can be treated with a high degree of accuracy using modern computational methods based first-order perturbation theory. In other cases, however, such as for optical transitions in indirect-gap materials, direct processes are forbidden by energy and momentum conservation, and the dominant indirect processes are enabled by the additional momentum provided by phonons. In this talk, I will present our work on the development and application of first-principles computational methods and codes for the predictive study of phonon-mediated quantum processes in semiconducting materials. I will discuss how phonons enable light absorption in indirect-gap semiconductors such as Si, BAs, and SiC, as well as how phonon-mediated transitions introduce optical loss in metals and doped semiconductors. I will also present our work on the phonon-mediated radiative recombination of excitons in indirect-gap semiconductors, and how these phonon-assisted processes in indirect-gap materials such as hexagonal BN can be as strong or even stronger than in direct-gap semiconductors. Last, I will also present our methodology for the study of non-radiative Auger-Meitner recombination in semiconductors, and how phonons are crucial to accurately quantify the non-radiative loss in silicon solar cells and in nitride optoelectronic devices. Our work sheds light on the intrinsic energy-conversion and loss mechanisms that are at work in modern semiconducting materials, and can propose avenues to alleviate them and improve the efficiency of devices. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D59.00002: How Spin Relaxes in Bulk Halide Perovskites Kejun LI, Junqing Xu, Uyen Huynh, Jinsong Huang, Valy Z Vardeny, Ravishankar Sundararaman, Yuan Ping Spintronics in halide perovskites has drawn significant attention in recent years, due to highly tunable spin-orbit fields and intriguing interplay with lattice symmetry. Spin lifetime -- a key parameter that determines the applicability of materials for spintronics and spin-based quantum information applications -- has been extensively measured in halide perovskites, but not yet assessed from first-principles calculations. Here, we leverage our recently-developed ab initio density-matrix dynamics framework [1, 2] to compute the spin relaxation time T1 and ensemble spin dephasing time T2 in a prototype halide perovskite, namely CsPbBr3 with self-consistent spin-orbit coupling and quantum descriptions of the electron scattering processes. We also implement the Lande g-factor for solids from first principles and take it into account in our dynamics, which is required to accurately capture spin dephasing under external magnetic fields. We thereby predict intrinsic spin lifetimes as an upper bound for experiments, identify the dominant spin relaxation pathways, and evaluate the dependence on temperature, external fields, carrier density, and impurities. Importantly, we find that the Fröhlich interaction that dominates carrier relaxation contributes negligibly to spin relaxation, consistent with the spin-conserving nature of this interaction. Our theoretical approach may lead to new strategies to optimize spin and carrier transport properties in spintronics and quantum information applications. [1] Xu et al., Nat. Commun., 11, 2780, (2020). [2] Xu et al., Phys. Rev. B, 104, 184418, (2021). |
Monday, March 6, 2023 3:48PM - 4:00PM |
D59.00003: Effect of phonon scattering on exciton transport in solid pentacene Galit Cohen, Diana Y Qiu, Sivan Refaely-Abramson Exciton decay and diffusion mechanisms are rooted in material structure and linked to the electronic, excitonic, |
Monday, March 6, 2023 4:00PM - 4:12PM |
D59.00004: Phonon screening of excitons with the ab initio GW-Bethe-Salpeter equation approach and Wannier interpolation Antonios Alvertis, Jonah B Haber, Zhenglu Li, Steven G Louie, Marina R Filip, Jeffrey B Neaton Exciton properties are critical to the optoelectronic response of materials, and can be described accurately within many-body perturbation theory (MBPT) and specifically the ab initio GW-Bethe-Salpeter (BSE) equation approach. It is however increasingly recognized that rigorous inclusion of lattice vibrations is critical to describe exciton physics, as phonons can significantly screen exciton binding energies [1]. Here we present a first-principles approach based on MBPT, building on the framework introduced in prior work [1], to compute the phonon screening of excitons entirely from first principles [2]. To do so we combine exciton properties from GW-BSE with electron-phonon interactions computed by employing Wannier interpolation methods, by utilizing a novel scheme that resolves gauge inconsistencies between these quantities [3], allowing us to increase computational efficiency by several orders of magnitude and demonstrate convergence for the phonon-screened exciton binding energy in a variety of semiconductors. This work is supported by the Center for Computational Study of Excited-State Phenomena in Energy Materials (C2SEPEM), supported by Basic Energy Sciences within the Office of Science in the US Department of Energy. Computational resources provided by NERSC. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D59.00005: Strain Effects on Auger-Meitner Recombination in Silicon Kyle M Bushick, Emmanouil Kioupakis Auger-Meitner 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). Due to silicon's conduction band valley degeneracy, strain engineering offers a possible route to tune this intrinsic recombination mechanism. In this work, we use first principles methods to quantify the effects of biaxial strain on both the direct and phonon-assisted Auger-Meitner recombination. Our analysis reveals a competition between the initial distribution of electrons across all six conduction band valleys in the unstrained case with increased occupation in the lower energy valleys upon the application of strain. This competition leads to an increase in the potency of the intravalley recombination processes compared to the perpendicular valley (f-type) configuration. Furthermore, we find that as in the unstrained material, the phonon-assisted process remains dominant under strained conditions. This work offers insight into a possible engineering route to adjust the intrinsic non-radiative recombination rate, which affects the overall efficiency for devices such as silicon solar cells. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D59.00006: Relations between T1 and T2 for spin systems with electron-phonon scattering Mani Chandra, Junqing Xu, Adela Habib, Christian Multunas, Joshua Quinton, Yuan Ping, Ravishankar Sundararaman A critical requirement for the realization of spintronic devices is the longevity of a spin-polarized ensemble, characterized by the T1 timescale. Meanwhile, the coherence of the spin ensemble is characterized by the T2 timescale, which can be very different from T1, and is vital for quantum information applications. Using ab initio real-time density-matrix dynamics within a Lindbladian framework that includes quantum scatterings, we compute the T2 timescales for a range of materials subject to electron-phonon scattering. The materials span both isotropic and anisotropic systems, as well as both Elliot-Yafet and Dyakonov-Perel relaxation mechanisms. We show that T2, for electron-phonon scattering, can be understood simply as an extension of T1 with appropriate averaging over the directions that the spins rotate in. We then deduce a number of identities relating T1 and T2. Importantly, in the presence of magnetic field inhomogeneities (either in real or k-space), a spin ensemble can dephase, characterized by the timescale T2*. Dephasing is distinct from decoherence since it can be reversed using a spin echo measurement. Our real-time framework enables a simulation of the spin echo setup, which we use to illustrate the relationship between the spin echo and the dephasing magnetic fluctuations in a simple model system. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D59.00007: Spin decoherence and dephasing in crystals from first principles Joshua S Quinton, Mani Chandra, Junqing Xu, Yuan Ping, Ravishankar Sundararaman Advances in spintronics and spin-based quantum information applications require a precise understanding of electron spin dynamics in condensed matter systems. Spin dynamics is typically characterized by time scales T1 for relaxation, T2 for decoherence and T2* for decoherence including inhomogeneous broadening induced spin dephasing. While these time scales are measured experimentally and estimated from model spin Hamiltonians, predicting them from first principles to identify the limiting spin properties of new materials has remained a challenge. Here, we present direct real-time simulations of Hahn spin echo measurements using a first-principles density-matrix dynamics approach. We investigate a range of systems spanning from semi-metallic graphene to halide-perovskite semiconductors and distinguish between T2 and T2* from the spin-echo simulations. We show that the impact of Lande g-factor fluctuations on dephasing in the intrinsic spin-phonon dynamics varies dramatically across systems of varying electronic structure, symmetry, and dimensionality. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D59.00008: First-Principles Calculations of Polarons in Rutile and Anatase TiO2 Zhenbang Dai, Chao Lian, Jon Lafuente-Bartolome, Feliciano Giustino Titanium dioxide (TiO2) has been an important technological material in many applications, such as photocatalysis and solar cells, but the polaronic nature of its charge carriers remains debatable despite few-decades theoretical and experimental investigation. Here, employing the newly developed method by our group, we report a systematic numerical study on the two most common polymorphs of TiO2, rutile and anatase phase. The adopted method can bypass the requirement of using a large supercell and eliminate the self-interaction error when doing DFT simulations of polarons, two shortcomings that are often blamed for the compromised reliability of modeling of polarons. With the new methodology, we will compute the electron- and hole-polaron formation energies, electronic wave functions, lattice distortions, and their spectral decompositions into individual Bloch states and phonon modes, shedding light on the most important factors influencing the polaronic physics of TiO2. Meanwhile, we will demonstrate how the addition of Hubbard U correction, a common practice when modeling polarons in TiO2, will impact calculation results in the context of new methodology. |
Monday, March 6, 2023 5:00PM - 5:12PM |
D59.00009: Ab initio many-body theory of polarons at all couplings Jon Lafuente-Bartolome, Chao Lian, Weng Hong Sio, Idoia G Gurtubay, Asier Eiguren, Feliciano Giustino State-of-the-art ab initio theories to describe polarons in materials currently fall into two separate categories: the weak coupling perturbative methods that describe phonon-induced band structure renormalizations, and the strong coupling adiabatic techniques that capture polaron self-trapping effects. The transition region between these regimes remains unclear. In this talk we present a self-consistent many-body theory of polarons that captures both limits and the intermediate regime within a single unified framework. The connection with previous literature on polaron models will be established, and practical first-principles calculations of the zero-point renormalization of band gaps including polaron localization effects will be presented. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D59.00010: Coherent Phonon Driven Carrier Pumping in Topological Materials Tao Jiang, Peter P Orth, Lin-Lin Wang, Feng Zhang, Cai-Zhuang Wang, Kai-Ming Ho, Jigang Wang, Yong-Xin Yao Laser-stimulated coherent phonon as a modulated strain field can modify ground state topological properties of quantum materials. Using real-time time-dependent density functional theory, we show that accompanying the periodic topological switching, carriers can be gradually pumped from valence band to conduction band despite the orders of magnitude smaller of the phonon energy relative to the insulating gap. This is achieved through the Landau-Zener tunnelling in certain region of the irreducible Brillouin zone where the transient energy gap becomes sufficiently small. The simulation results are consistent with the recent pump-probe experiment on the topological insulator ZrTe5 at low temperature. |
Monday, March 6, 2023 5:24PM - 5:36PM |
D59.00011: Topological behavior in a solvable 3D model Tian Xue, Zhiyuan Wang, Eduardo Ibarra-García-Padilla, Kaden Hazzard Recently, arxiv:2202.11303 discovered a solvable classical 3D model that has topological behavior, with loop observables -- products of spins on loops -- that depend on only their topology. Specifically, averages of non-contractible loops vanish while contractible loops average to one. However, because the model is solvable only at special points, the robustness of these observations has remained unknown. In this talk, I will show that the loop observables are robust to perturbations over ranges of temperatures and loop sizes that are large when the perturbation is small. I will present arguments for these claims, and show quantitative evidence using numerically exact calculations using Monte Carlo methods, with custom Monte Carlo moves to ensure ergodic sampling of configurations. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D59.00012: Ab Initio Maximally-Localized Exciton Wannier Functions for Solids Jonah B Haber, Felipe H Jornada, Diana Y Qiu, Jeffrey B Neaton Since their introduction nearly 25 years ago, maximally-localized Wannier functions (MLWFs) have contributed significantly to many areas of electronic structure theory, impacting our ability to understand both local (chemical bonding) and global (topological) properties of solid-state systems. However, to date the MLWF framework has been applied to single-particle excitations. Excitons, correlated electron-hole pairs, dominate the optical response in gapped materials and understanding these composite particles plays an important role in the design of next-generation optoelectronic devices. Here, we leverage the MLWF scheme to construct maximally localized exciton Wannier functions (MLXWFs), representations of two-particle electron-hole states where the gauge freedom is used to enforce localization in the average electron-hole coordinate. As a proof-of-concept, we apply our framework to low-lying singlet and triplet excitons, computed with the ab initio GW plus Bethe-Salpeter approach, in the ionic solid LiF. We plot the MLXWFs and detail the convergence of their spreads. Our work paves the way towards the ab initio construction of exciton tight binding models, efficient interpolation of the exciton-phonon vertices, computation of the Berry-curvature for exciton bands, and more. |
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