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 B61: Electrons, Phonons, Electron-Phonon Scattering and Phononics IFocus
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Sponsoring Units: DCOMP Chair: Christoph Heil, Graz University of Technology Room: Room 418 |
Monday, March 6, 2023 11:30AM - 12:06PM |
B61.00001: Phonon second sound over 200 K and cubic boron arsenide as a superior semiconductor Invited Speaker: Gang Chen This talk will report our observations of phonon second sound over 200K in graphite, and the simultaneously high phonon thermal conductivity, and electron and hole mobilities in cubic boron arsenide. The experimental studies were stimulated by first-principles based simulations on electron and phonon transport. Direct solutions of the phonon Boltzmann transport equation, including the full scattering matrix obtained from first-principles simulations of phonon-phonon scattering, predicted the existence of phonon hydrodynamic transport at high temperatures. Our experiments using transient grating setup observed second sound, the collective thermal transport of phonons as waves, over 200 K. Our experiments and simulations also show the co-existence of thermal zero sound—the thermal waves due to ballistic phonons. The talk will then shift to phonon and electron transport in cubic boron arsenide. First-principles simulations, including 3- and 4-phonon scattering processes, and electron-phonon interaction, predicted that the special phonon band structure of cubic boron arsenide lead to very high phonon thermal conductivities, and simultaneously high electron and hole mobilities. These predictions were confirmed by experiments, with measured room-temperature thermal conductivity over 1200 W/m-K, and ambipolar mobility over 1600 cm2/s. With a bandgap ~2 eV, these properties position the cubic boron arsenide as the best semiconductor. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B61.00002: Low and high field ambipolar mobility in BAs based on two phonon scattering Iretomiwa Esho, Austin J Minnich Boron Arsenide (BAs) has drawn significant interest due to its high thermal conductivity and ambipolar charge mobility [1, 2]. These properties make BAs a promising candidate electronic material for future technological applications. Recently, higher-order electron-phonon scattering processes in polar and non-polar semiconductors have been reported to have a non-negligible impact on charge transport [3, 4, 5]. Here, we report an ab initio study of two-phonon electron and hole scattering processes in BAs at both low and high electric fields. We find that inclusion of these higher-order processes significantly reduces the computed low and high field charge carrier mobility by 20-30%. One and two-phonon processes involving longitudinal optical phonons are found to have little effect on either low and high-field transport properties owing to the high optical phonon energy relative to thermal charge carrier energies. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B61.00003: High-performance modeling of electron and phonon transport using Phoebe Jennifer Coulter, Andrea Cepellotti, Anders Johansson, Boris Kozinsky The theoretical prediction of electrical and thermal transport properties relies on an accurate description of the electrons, phonons, and their interactions must be considered to accurately predict transport behavior. While first-principles methods based on density functional theory can describe these material-specific quasiparticle properties, using this information to calculate transport coefficients can be computationally demanding. To address this challenge, we developed Phoebe (https://mir-group.github.io/phoebe/), which includes the effects of electron-phonon and phonon-phonon interactions to predict the transport properties of materials by solving the Boltzmann transport equation (BTE) using a full scattering matrix formalism. In this talk, I will report on ongoing new features of Phoebe, including the addition of magnetotransport calculations as well as new tutorials and updated performance benchmarks. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B61.00004: Fully Anharmonic Thermoelectric Efficiencies from First Principles Christian Carbogno, Kisung Kang, Jingkai Quan, Matthias Scheffler The computational design of improved materials with optimal thermoelectric efficiency zT requires to tailor both the electronic and the vibrational transport coefficients. With respect to the latter, ab initio molecular dynamics (aiMD) calculations have revealed that strongly anharmonic effects associated to short-lived distortions are highly beneficial for increasing zT. [1] However, an accurate first-principles assessment of electronic transport is challenging when such strongly anharmonic effects are active, since different electronic conduction mechanism can compete in this regime. In this work, we overcome this hurdle by combining approaches suited for assessing ionic conductivities, i.e., the Berry phase formalism, with temperature-dependent electronic-structure theory approaches [2] suited for assessing band-type transport in semiconductors. In turn, this allows to evaluate electronic fluxes along aiMD trajectories und to utilize the Green-Kubo formula to obtain accurate transport coefficients for arbitrarily anharmonic semi-conductors. |
Monday, March 6, 2023 12:42PM - 12:54PM |
B61.00005: Nonadiabatic Born effective charges in metals and the Drude weight Cyrus E Dreyer, Sinisa Coh, Massimiliano Stengel In insulators, Born effective charges describe the electrical polarization induced by the displacement of individual atomic sublattices. Such a physical property is at first sight irrelevant for metals and doped semiconductors, where the macroscopic polarization is ill-defined. Here we show that, in clean conductors, going beyond the adiabatic approximation results in nonadiabatic Born effective charges that are well defined in the low-frequency limit. In addition, we find that the sublattice sum of the nonadiabatic Born effective charges does not vanish as it does in the insulating case, but instead is proportional to the Drude weight. We demonstrate these formal results with density functional perturbation theory calculations of Al, and electron-doped SnS2 and SrTiO3. |
Monday, March 6, 2023 12:54PM - 1:06PM |
B61.00006: Ab-initio high-field transport and noise in p-Si: low temperatures and high frequencies David Catherall, Austin J Minnich The cryogenic transport properties of hot holes in silicon exhibit several anomalies, including an additional saturated drift velocity regime and a non-monotonic trend of the microwave-frequency current noise versus electric field. Despite prior investigations, these observations lack generally accepted explanations. Here, we examine the microscopic origin of these phenomena by extending the ab-initio theory of high-field transport and noise in semiconductors. We find that the drift velocity anomaly may be attributed to scattering dominated by acoustic phonon emission, leading to an extra regime of drift velocity saturation at low temperatures; while the non-monotonic trend in the current noise arises due to the decrease in momentum relaxation time with electric field. The former conclusion is consistent with the findings of a prior work, but the latter distinctly differs from previous explanations which invoked energy relaxation as the origin. This work highlights the use of high-field transport and noise phenomena as sensitive probes of microscopic charge transport phenomena in semiconductors. |
Monday, March 6, 2023 1:06PM - 1:18PM |
B61.00007: Conductivity predictions for warm dense beryllium from first principles Brian Robinson, Andre Schleife, Stephanie B Hansen, Alina Kononov, Andrew D Baczewski Accurate understanding of scattering processes in the warm dense matter (WDM) regime leads to improvements in electrical and thermal conductivity predictions that are essential in the design of inertial confinement fusion (ICF) experiments. In our approach, we use first-principles calculations to study electron-electron (e-e) and electron-phonon (e-ph) scattering processes in warm dense beryllium with near solid density and electronic temperatures greater than 0.5 eV. The standard method for WDM conductivity calculations, based on the Kubo-Greenwood formula, does not properly describe e-e or e-ph scattering processes. We calculate e-e lifetimes by fitting the imaginary part of the self-energy from many-body perturbation theory GW calculations to the Landau theory of the Fermi liquid, where we find the fitting parameter to be 0.018 eV-1. We also study the carrier dynamics of excited electrons, represented by a Gaussian distribution of the Kohn-Sham states, centered 1-3 eV above the Fermi energy, arising from e-ph scattering, via solving the Bolzmann transport equation (BTE). This yields predictions of quantities such as relaxation times towards a Fermi distribution. We estimate that our results could alter predictions used to model ICF experiments by about a factor of two. |
Monday, March 6, 2023 1:18PM - 1:30PM |
B61.00008: Electronic Transport in two-dimensional 2D- MXenes for Energy Storage Nesrine Boussadoune, Olivier Nadeau, Gabriel Antonius Two-dimensional flexible supercapacitors may offer environment-friendly energy storage for high-power usage. MXenes, are a new family of 2D materials with a general formula of Mn+1XnTx where M is a transition metal, X is carbon and/or Nitrogen, and T represents the surface terminations group (O, F, OH). This 2D hexagonal family has been shown to be a potential electrode material for SCs, due to its large active surface area, and excellent electrical conductivity. In this work, we investigate the electronic and vibrational properties of pristine Ti3C2 and fully terminated (Ti3C2F2, Ti3C2(OH)2, Ti2CF2) using first-principles calculations. Our goal is to understand how the electronic transport properties depend on the chemical composition and surface termination using density functional theory (DFT), density functional perturbation theory (DFPT), and the linearized Boltzmann transport equation (LBTE) within the relaxation time approximation (RTA). We present a detailed study of the convergence behavior of the electrical conductivity in these systems, we compare the different levels of approximations and discuss techniques to reduce the computational cost of our calculations. |
Monday, March 6, 2023 1:30PM - 1:42PM |
B61.00009: Ab-initio piezoresistivity and intervalley scattering in n-Si Benjamin Hatanpaa, Austin J Minnich The relative contribution of f- and g-type intervalley scattering processes in Si, corresponding to scattering to inequivalent and equivalent valleys, respectively, has been a topic of debate for many decades. Although typical transport properties are not able to distinguish these processes, the piezoresistivity and the diffusion coefficient are notable exceptions. Ab-initio calculations of such properties provide a means to resolve this controversy, but the computed transport properties of Si under uniaxial stress have not been extensively reported. Here, we calculate the piezoresistivity and diffusion coefficient of Si from first principles at various temperatures and crystallographic orientations. The calculations and comparison with experiment allow for the relative contribution of f- and g-type intervalley scattering to be rigorously assessed. |
Monday, March 6, 2023 1:42PM - 1:54PM |
B61.00010: Many-body theory of phonon-induced spin relaxation and decoherence Jinsoo Park, Yao Luo, Jin-Jian Zhou, Marco Bernardi First-principles calculations enable accurate predictions of electronic interactions and dynamics. However, computing the electron spin dynamics remains challenging. The spin-orbit interaction causes various dynamical phenomena that couple with phonons, such as spin precession and spin-flip e-ph scattering, which are difficult to describe with current first-principles calculations. In this talk, we present a rigorous framework to study phonon-induced spin relaxation and decoherence, by computing the spin-spin correlation function and its vertex corrections due to e-ph interactions [1,2]. We apply this approach to a model system and develop corresponding first-principles calculations of spin relaxation in GaAs. These calculations show that our vertex-correction formalism can capture the Elliott-Yafet, Dyakonov-Perel, and strong-precession mechanisms - three independent spin decoherence regimes with distinct physical origins - thereby unifying their theoretical treatment and calculation. Our method is general and enables quantitative studies of spin relaxation, decoherence, and transport in a wide range of materials and devices. |
Monday, March 6, 2023 1:54PM - 2:06PM |
B61.00011: First-principles analysis of charge transport and spin relaxation in germanium Shaelyn Iyer, Jinsoo Park, Marco Bernardi Germanium is an emerging candidate material for quantum technologies due to its high carrier mobility and strong spin-orbit coupling (SOC). Existing studies of charge transport and spin relaxation in Ge have focused on phenomenological models and qualitative understanding. Leveraging advances in first-principles methods, more quantitative studies of the interactions of carriers and spin with phonons are now possible. In this talk, we present a first-principles study of phonon-limited charge transport and T1 spin relaxation times in bulk Ge. Our calculations employ an accurate band structure obtained from hybrid functionals and electron-phonon interactions that include SOC via fully-relativistic pseudopotentials. We solve the Boltzmann transport equation to study transport and our recently developed spin-phonon Bethe-Salpeter equation for spin dynamics [1], in both cases using the PERTURBO code [2]. Our computed mobilities and T1 spin relaxation times are in excellent agreement with experiments in the 100 – 300 K temperature range for both electron and hole carriers. By analyzing the contributions from different phonon modes and electronic valleys, we demonstrate that charge transport and spin relaxation are governed by distinct microscopic mechanisms. The effect of external strain on the mobility and spin relaxation times will also be discussed. Our work sheds light on microscopic electron and spin dynamics in Ge, aiding the development of future Ge-based quantum technologies. |
Monday, March 6, 2023 2:06PM - 2:18PM |
B61.00012: Coherent charge carrier dynamics in the presence of thermal lattice vibrations Donghwan Kim, Alhun Aydin, Alvar Daza, Kobra N Avanaki, Joonas Keski-Rahkonen, Eric J Heller We develop the coherent state representation of lattice vibrations to describe their interactions with charge carriers. In direct analogy to quantum optics, the coherent state representation leads from quantized lattice vibrations (phonons) naturally to a quasiclassical field limit, i.e., the deformation potential. To an electron, the deformation field is a sea of hills and valleys, as ``real'' as any external field, morphing and propagating at the sound speed, and growing in magnitude with temperature. In this disordered potential landscape, the charge carrier dynamics is treated nonperturbatively, preserving their coherence beyond single collision events. We show the coherent state picture agrees exactly with the conventional Fock state picture in perturbation theory. Furthermore, it goes beyond by revealing aspects that the conventional theory could not explain: transient localization even at high temperatures by charge carrier coherence effects, and band tails in the density of states due to the self-generated disorder (deformation) potential in a pure crystal. The coherent state paradigm of lattice vibrations supplies tools for probing important questions in condensed matter physics as in quantum optics. |
Monday, March 6, 2023 2:18PM - 2:30PM |
B61.00013: The electron mobility of SnO2 from first principles Amanda X Wang, Kyle M Bushick, Nick Pant, Woncheol Lee, Xiao Zhang, Samuel Poncé, Joshua A Leveillee, Feliciano Giustino, Emmanouil Kioupakis The transparent semiconducting oxide SnO2 is a wide-band-gap semiconductor often used in its doped form in various optoelectronic devices. The experimentally measured electron mobility values in the literature vary widely depending on the growth conditions and doping concentrations. In this work, we investigate the dependence of the phonon-limited electron mobility on temperature and free electron concentration from first principles. We explore the contribution of the different phonon modes to electron scattering to understand how the band structure and phonon dispersion determine the fundamental limits of electron transport in SnO2. Band structures and electron-phonon coupling strengths are calculated from first principles with density functional theory and density functional perturbation theory respectively, with quasiparticle effects and quadrupole corrections applied to ensure accuracy. We compare our calculated mobility values with experimental results and discuss the implications for future applications of this material. |
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