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 D50: Electron-phonon coupling effects on optical spectra: theory and applicationsInvited
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Sponsoring Units: DCOMP Chair: Yuan Ping, University of California, Santa Cruz Room: Room 320 |
Monday, March 6, 2023 3:00PM - 3:36PM |
D50.00001: Phonon-assisted linear and non-linear optical processes from first principles Invited Speaker: Xiao Zhang The predictive understanding of phonon-assisted optical processes provides essential information on the functionality of indirect-band-gap materials in optoelectronic applications, as well as on the optical response of materials in the presence of free carriers. Recent methodological developments based on maximally localized Wannier functions have enabled the efficient calculation of the electron-phonon and the electron-photon coupling matrix elements with fine sampling of the Brillouin zone, and have catalyzed detailed investigations of the phonon-assisted indirect optical processes in materials. In this talk, I will discuss our recent advances of perturbation-theory-based theoretical characterization of phonon-assisted linear and nonlinear optical processes in both insulating and conducting materials. I will first discuss the general formalism based on second-order perturbation theory to model phonon-assisted optics. I will show that second-order perturbation theory accurately predicts the phonon-assisted absorption spectra of indirect-band-gap materials such as silicon and silicon carbide. Further, I will show that the formalism can be extended to study optical absorption by free carriers in doped semiconductors such as silicon, and metals such as silver and gold. Our results are in excellent agreement with experimental measurements, and explain the dominant absorption mechanisms at different photon wavelengths. Our work allows us to analyze the origin of optical losses in infrared optoelectronic devices and enables the design of new plasmonic materials. Last, I will present our recent development to characterize phonon-assisted two-photon absorption using higher-order perturbation theory, and I will discuss the limitation of perturbative approaches to phonon-assisted optics as well as ways to overcome them. |
Monday, March 6, 2023 3:36PM - 4:12PM |
D50.00002: Impact of Phonons on Electron-Hole Interactions in Semiconductors and Insulators. Invited Speaker: Marina R Filip
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Monday, March 6, 2023 4:12PM - 4:48PM |
D50.00003: The special displacement method as a unified treatment of anharmonicity and electron-phonon coupling in solids Invited Speaker: Marios Zacharias Including quantum nuclear effects in electronic structure calculations of solids has been the focus of intensive research over the last decade. These effects drive electron-phonon and phonon-phonon couplings, playing a key role in addressing compelling scientific questions in condensed matter physics [1]. For example, quantum nuclear dynamics leads to the zero-point renormalization of electron energy levels, as well as to phonon-assisted optical transitions and transport coefficients [1]. In this talk, I will discuss first how the recent advances in nonperturbative supercell calculations can account separately for electron-phonon and phonon-phonon interactions. Then, I will present the special displacement method (SDM) [2,3] as a unified approach to the many-body problem and show some of its capabilities, including the calculation of temperature-dependent anharmonic phonons, band structures, absorption coefficients, and exciton-phonon spectra. I will demonstrate that SDM is designed to replace the vibrational sampling performed in Monte Carlo or Molecular dynamics simulations [5] to the point that only a single thermal nuclei configuration is enough for obtaining accurate results. Applications of SDM for typical semiconductors, 2D materials, perovskites, and quantum dots will be discussed [2,3,4,5,6]. I will also explain the physical concepts hidden in SDM, discuss its merits and drawbacks, and indicate avenues for future work in ab-initio calculations at finite temperatures. Finally, I will present our recent work on the role of polymorphism and anharmonicity in the vibrational properties and electron-phonon physics of cubic perovskites [6]. |
Monday, March 6, 2023 4:48PM - 5:24PM |
D50.00004: The Impact of Electron-Phonon Interactions in Monolayer Materials from First-Principles Invited Speaker: Sahar Sharifzadeh We utilize first-principles theory to investigate the optoelectronic properties of a series of monolayer materials, emphasizing the role of electron-phonon interactions, a phenomenon that can dominate the properties of low dimensional systems due to their reduced screening. We utilize first-principles density functional theory (DFT) and many-body perturbation theory (MBPT) to describe excited state transitions and the special displacement (SD) method recently developed by Zacharias and Giustino to describe the role of phonons. For monolayer GeSe, a promising monochalcogenide material, our calculations predict that the optical absorption spectrum is red-shifted by ~ 0.1 eV and that the Wannier exciton wavefunction is distorted due to electron-phonon interactions, with optical phonons at ~100 cm-1 coupling most strongly to the excitonic state. To better understand the role of exciton-phonon interactions in low dimensions, we study the band gap renormalization for a series of 2D materials. For ~100 monolayer materials, we compute the gap with and without the presence of phonons within DFT and the SD approach. The connection between different physical descriptors with band gap renormalization are explored and highlighted using a data-driven approach, demonstrating that the strength of electron-phonon interactions is highly dependent on the bonding structure. Overall, this framework allows for a systematic theoretical exploration of the influence of phonons on optical properties. |
Monday, March 6, 2023 5:24PM - 6:00PM |
D50.00005: High-throughput computations of phonon-limited electronic transport Invited Speaker: Geoffroy Hautier The last decade has seen significant developments in our capability to model transport processes limited by phonons such as mobility, conductivity or Seebeck coefficients. A full ab initio treatment of electronic transport within Boltzmann transport formalism and taking into account electron-phonon coupling is now possible and has been demonstrated for several important materials. These fully ab initio computations are however computationally expensive and most importantly require in general a very dense k-point mesh obtained through Wannierization, a process that is not always trivial and challenging to automatize. |
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