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 K59: First-Principles Simulations of Excited-State Phenomena: Electron-phonon Interactions IIFocus
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Sponsoring Units: DCOMP Chair: Yuan Ping, University of California, Santa Cruz Room: Room 301 |
Tuesday, March 7, 2023 3:00PM - 3:36PM |
K59.00001: The interaction of electrons and excitons with phonons in solids: Results from model problems and ab initio calculations. Invited Speaker: David Reichman In this talk I will discuss several perspectives on the modeling of the interactions between charge carriers and phonons in solids. In the first part of the talk I will present a novel mhechanism for electron-phonon interactions in solids that is shown by exact quantum Monte Carlo calculations to lead to relatively high superconducting transition temperatures in the dilute carrier limit. In the second part of the talk, I will discuss the ab initio modeling of polarons and excitonic polarons in solids. |
Tuesday, March 7, 2023 3:36PM - 3:48PM |
K59.00002: Ultrafast phenomena in diamond and silicon in the presence of crystal defects Tobias Zier, Marie Kempkes, David A Strubbe Femtosecond-laser pulses can induce extreme conditions in solid systems, which causes a variety of ultrafast phenomena, like ultrafast melting or thermal phonon squeezing, a coherent atomic motion. Underlying reason for those laser-induced atomic effects are changes in the interatomic bonding due to the highly excited electron system. However, crystal vacancies already change the local bonding properties in the ground state. In order to analyze ultrafast phenomena in the presence of crystal defects we used finite temperature DFT to perform ab initio MD simulations of silicon and diamond with a defect density of up to 3%. Our results show for intensities well below the laser-melting threshold an increase of the normalized Bragg peak intensity for both materials, an indication for defect annealing. At moderate intensities close to but below the melting threshold, we show that the frequency and the amplitude of thermal phonon squeezing can be manipulated by the defect density. For high intensities well above the melting threshold, the atoms follow different atomic pathways during nonthermal melting than in the perfect crystal. |
Tuesday, March 7, 2023 3:48PM - 4:00PM |
K59.00003: Vibrationally resolved optical excitations of the nitrogen-vacancy center in diamond Yu Jin, Marco Govoni, Giulia Galli A comprehensive description of the optical cycle of spin defects in solids requires the understanding of the electronic and atomistic structure of states with different spin multiplicity, including singlet states which are particularly challenging from a theoretical standpoint. We present a general framework, based on spin-flip time-dependent density function theory implemented in the WEST code, to determine the excited state potential energy surfaces of the many-body singlet states of spin defects; we then predict the vibrationally resolved absorption spectrum between singlet shelving states of a prototypical defect, the nitrogen-vacancy center in diamond [1]. Our results, which are in excellent agreement with experiments, provide an interpretation of the measured spectra and reveal the key role of specific phonons in determining absorption processes, and the notable influence of non-adiabatic interactions. The insights gained from our calculations may be useful in defining strategies to improve infrared-absorption-based magnetometry and optical pumping schemes. The theoretical framework developed here is general and applicable to a variety of other spin defects and materials. |
Tuesday, March 7, 2023 4:00PM - 4:12PM |
K59.00004: Ab-initio theory of spin-phonon relaxation for paramagnetic defects in semiconductors Matthew C Cambria, Ariel Norambuena, Yanfei Li, Hossein Dinani, Gergo Thiering, Aedan Robert H Gardill, Ishita Kemeny, Vincenzo Lordi, Adam Gali, Jeronimo R Maze, Shimon Kolkowitz The theory of spin-lattice relaxation in solids were originally developed back in the 60's by pioneering work of Orbach [1] and various others. However, the ab-initio predictions for spin-phonon induced spin relaxation and dephasing are still a scarce. There are recent ab-initio studies [2] that discuss the spin-phonon interaction in molecular magnets with limited degrees of freedom, yet the ab-initio theory for paramagnetic defects in bulk materials is still lacking. Therefore, we will show the key elements of spin-phonon interaction in an exemplary nitrogen-vacancy (NV) center of diamond and depict the second-order Raman processes that governs the spin-lattice interaction within its |ms=0〉, |ms=±1〉 spin triplet manifold and also the main contributor in temperature dependence of zero-field splitting. We will show a novel spectral function formalism that incorporates both the continuous aspects of phonons and finite nature of point defects. In summary, our present method predicts spin T1 and T2 times for defects comparable to that of experiments [3]. |
Tuesday, March 7, 2023 4:12PM - 4:24PM |
K59.00005: Unified first-principles description of direct and phonon-assisted optical absorption Sabyasachi Tiwari, Emmanouil Kioupakis, Feliciano Giustino Current state-of-the-art ab initio approaches to study optical absorption can describe direct absorption processes for direct bandgap materials, and phonon assisted indirect absorption processes for indirect bandgap materials. One limitation of these approaches is that the formalism for phonon-assisted absorption becomes ill-defined for photon energies exceeding the direct band gap, therefore many materials where direct and indirect gaps are close in energy cannot be described adequately. In this talk, we present a new many-body formalism to capture both direct and phonon-assisted processes on the same footing. We demonstrate this approach by discussing a few test cases, such as silicon, gallium arsenide, and germanium. |
Tuesday, March 7, 2023 4:24PM - 4:36PM |
K59.00006: First-principles calculations of charge carrier mobility in semiconductors including charged impurity scattering Joshua A Leveillee, Xiao Zhang, Emmanouil Kioupakis, Feliciano Giustino Ionized impurities are present in and strongly effect the behaviors of semiconductors in a wide variety of electronic and opto-electronic devices. Ionized impurities generate long-range scattering centers that reduce the electron and hole mobilities. Though a variety of historical models are available to predict carrier mobility as a function of ionized impurity concentration, first-principles calculations offer a way to more accurately describe the physics of ionized impurity scattering in a variety of materials. In this work, we calculate from first principles the electron and hole mobilities and scattering rates limited by both carrier-phonon and carrier-ionized impurity scattering in three prominent semiconductor materials: Si, 3C-SiC, and GaP. We show that the influence of ionized impurity scattering and its balance with phonon scattering are strongly material dependent and influence the expected carrier mobilities as a function of impurity concentration and temperature. Further, we show how the Matthiessen's rule for carrier mobilities limited by different scattering mechanisms breaks down outside of the constant relaxation time approximation. Lastly, we demonstrate the importance of screening and effective mass corrections on calculated carrier mobilities. |
Tuesday, March 7, 2023 4:36PM - 4:48PM |
K59.00007: Ab initio study of polarons in the alkali halides Chao Lian, Jon Lafuente-Bartolome, Weng Hong Sio, Feliciano Giustino A charge carrier propagating through a crystal induces distortions in the lattice via the electron-phonon interaction. The quasiparticle formed by the carrier and the lattice distortion is referred to as a polaron. Recent advances have enabled the calculation of small and large polarons on the same footing from first principles [Phys. Rev. Lett. 122, 246403 (2019); Phys. Rev. Lett. 129, 076402 (2022)]. In this talk, we present a systematic application of these methods to a broad family of materials that span a very wide range of electron-phonon interaction strengths, the alkali halides. We show that these compounds consistently host large electron polarons and small hole polarons. By investigating how the coupling mechanism, formation energy, and polaron radius depend on materials properties such as dielectric constants, band gaps, and effective masses, we establish general scaling laws and we identify the validity range of standard polaron models. |
Tuesday, March 7, 2023 4:48PM - 5:00PM |
K59.00008: Data-driven solution of the real-time Boltzmann transport equation: speeding up and finding patterns in first-principles calculations of nonequilibrium dynamics Ivan Maliyov, Jia Yin, Chao Yang, Marco Bernardi The Boltzmann transport equation (BTE) is a convenient framework for studies of nonequilibrium dynamics in materials. We have recently shown that solving the real-time BTE (rt-BTE) by time-stepping the electron and phonon occupations enables first-principles studies of nonequilibrium dynamics of coupled electrons and phonons [1,2]. Variants of this formalism include ab initio electron-phonon (e-ph) and/or phonon-phonon (ph-ph) interactions, external electric fields, and even excitonic effects. However, a bottleneck of these methods is computing the BTE collision integrals, which requires dense momentum grids, leading to high computational cost even for simple materials. |
Tuesday, March 7, 2023 5:00PM - 5:12PM |
K59.00009: Toward First Principles Magnon-Phonon Interactions Khoa Le Collective spin excitations (magnons) in magnetic materials have been intensely investigated in recent years for their potential applications in spintronics and quantum information science. Lattice vibrations (phonons) couple with magnons and set an intrinsic limit to their lifetimes and coherent transport. In this talk, we will present an approach for computing magnon-phonon interactions from first principles. This method combines ab initio electron-phonon interactions with magnon wave functions obtained from the finite-momentum Bethe-Salpeter equation, leveraging an interface between the YAMBO and PERTURBO codes. We will present illustrative calculations of magnon-phonon coupling and magnon lifetimes due to phonons in two-dimensional (anti)ferromagnetic materials. Extensions of this formalism will also be discussed.
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Tuesday, March 7, 2023 5:12PM - 5:24PM |
K59.00010: Simulating electronic excitation induced proton transfer in heterogeneous environments Jianhang Xu, Ruiyi Zhou, Christopher Malbon, Tao E Li, Volker Blum, Sharon Hammes-Schiffer, Yosuke Kanai Excited-state intramolecular proton transfer (ESIPT) is one of the essential steps in solar energy conversion by many biological and chemical systems. In order to investigate such key dynamical processes from first principles, we newly developed a periodic real-time nuclear-electronic orbital time-dependent density functional theory (RT-NEO-TDDFT) method such that proton dynamics are treated quantum mechanically. In this work,we study how atomistic environments like water solvation and the presence of a material surface affect electron excitation-induced proton transfer in the o-hydroxybenzaldehyde (oHBA) molecule. Competing kinetics between electronic excitation dynamics and quantum-mechanical proton transfer are discussed as an example of how such a new multicomponent DFT formulation can expand the application of RT-TDDFT. |
Tuesday, March 7, 2023 5:24PM - 5:36PM |
K59.00011: Ultrafast charge dynamics and optical response in bilayer WSe2: impact of excitons and electron-phonon interaction Jia Shi, Volodymyr Turkowski, Talat S Rahman Transition metal dichalcogenides (TMDs) are well known as semiconductors with strong intra- and inter-layer interactions between electrons and holes and between charges and phonons, with promising potential for applications in energy harvesting to charge reusable batteries. We present here results of time-dependent density-functional theory, in the density-matrix implementation, combined with many-body theory for the charge dynamics and photoluminescence in bilayer WSe2 with AA'-stacking order that is excited by an ultrafast laser pulse. We find that because of electron- and the exciton-phonon scattering the charge dynamics occurs at the picosecond timescale in both the linear and nonlinear response regimes. Excitonic states, as the lowest-energy excited states with large transition dipole moments, play an important role in the charge dynamics and photoluminescence of the system. In particular, they contribute to the inter-valley dynamics of charges and generation of the third-order harmonic in the emission spectrum. Because of the long lifetimes of the dark inter-valley excitons, these states are especially important in the phenomena above. Obtained results may help to understand the details of the ultrafast optical response of charges in bilayers of TMDs that can be used in practical applications. |
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