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 GG05: V: Electrons, Phonons, Electron-Phonon Scattering and Phononics IFocus
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Sponsoring Units: DCOMP Chair: Rohit Goswami, Science Institute, University of Iceland & Quansight Labs,TX Room: Virtual Room 5 |
Monday, March 20, 2023 12:30PM - 1:06PM |
GG05.00001: Femto- phono- magnetism Invited Speaker: Sangeeta Sharma From the outset of research into femtomagnetism, the field in which spins are manipulated by light on femtosecond or faster time scales, several questions have arisen and remain highly debated: How does the light interact with spin moments? How is the angular momentum conserved between the nuclei, spin, and angular momentum during this interaction? What causes the ultrafast optical switching of magnetic structures? What is the ultimate time limit on the speed of spin manipulation? What is the impact of nuclear dynamics on the light-spin interaction? |
Monday, March 20, 2023 1:06PM - 1:18PM |
GG05.00002: Ultraweak electron-phonon coupling strength in cubic boron arsenideunveiled by ultrafast dynamics Zhenyun Tian We report a time-resolved ultrafast quasiparticle dynamics investigation of c-BAs, which is a recently discovered highly thermally conducting material. The excited-state ultrafast relaxation channels dictated by the electron-phonon coupling (EPC), phonon-phonon scattering, and radiative electron-hole recombination have been unambiguously identified, along with their typical interaction times. Significantly, the EPC strength is obtained from the dynamics, with a value of ?T2= 0.008 (corresponding to ?2> = 1.18 ± 0.08 ps–2), demonstrating an unusually weak coupling between the electrons and phonons. As a comparison, an ultraweak EPC strength for graphene is also expected. We propose that preserving an ultrasmall EPC strength may be a prerequisite for exhibiting an ultrahigh thermal conductivity. Our investigation provides insight for searching and designing ultrahigh thermal conductivity materials. Notably, during our analysis we have generalized the fluence-dependence method for obtaining the EPC strength to room temperature, which can be applied to many other types of quantum materials in the future. |
Monday, March 20, 2023 1:18PM - 1:30PM |
GG05.00003: Self-energy dynamics and the mode-specific phonon threshold effect in Kekulé-ordered graphene Hongyun Zhang, Changhua Bao, Shaohua Zhou, Michael Schüler, Thomas Devereaux, Shuyun Zhou Electron-phonon interaction and related self-energy are fundamental to both the equilibrium properties and non-equilibrium relaxation dynamics of solids. Although electron-phonon interaction has been suggested by various time-resolved measurements to be important for the relaxation dynamics of graphene, the lack of energy- and momentum-resolved self-energy dynamics prohibits direct identification of the role of specific phonon modes in the relaxation dynamics. Here, by performing time- and angle-resolved photoemission spectroscopy measurements on Kekulé-ordered graphene with folded Dirac cones at the Gamma point, we have succeeded in resolving the self-energy effect induced by the coupling of electrons to two phonons at Omega_1 = 177 meV and Omega_2 = 54 meV, and revealing its dynamical change in the time domain. Moreover, these strongly coupled phonons define energy thresholds, which separate the hierarchical relaxation dynamics from ultrafast, fast to slow, thereby providing direct experimental evidence for the dominant role of mode-specific phonons in the relaxation dynamics. |
Monday, March 20, 2023 1:30PM - 1:42PM |
GG05.00004: First-principles simulations of ultrafast phase transition in condensed-matter systems Mengxue Guan The crystal structure of a solid largely dictates its electronic, optical and mechanical properties. Laser driven structural engineering allows the manipulation of functional properties at high speed and beyond what maybe possible in equilibrium. We developed a first-principles approach (time-dependent ab initio propagation, TDAP) that aims at providing robust dynamic simulations of light-induced, highly nonlinear phenomena by real time calculation of combined photonic, electronic and ionic quantum mechanical effects within a time-dependent density functional theory (TDDFT) framework. By comparing the theoretical and experimental results, the approaches have been demonstrated effective and efficient in treating ultrafast quantum dynamical processes. |
Monday, March 20, 2023 1:42PM - 1:54PM |
GG05.00005: A study of nano-scale electron transport using the McKelvey-Shockley transport framework Qinxin Zhu Nano-scale electron transport plays an important role in electronic applications, including ultra- scaled and emerging nano-devices. While there are several approaches that can treat nano-scale transport, here we revisit the McKelvey-Shockley (McK-S) flux method, which is a computational efficient and physically transparent framework. This study focuses on reformulating the electron McK-S equations to resolve energy-dependent fluxes, capture the effect of electric field, and include a more rigorous treatment of electron-phonon scattering. This updated McK-S formalism is used to simulate electron transport across a finite-length semiconductor under the influence of constant electric field under varying conditions from ballistic to diffusive and from near-equilibrium to non-equilibrium and are benchmarked against solutions of the Boltzmann transport equation (BTE). The McK-S results display a good agreement with those of the BTE, with some notable differences that will be discussed. Looking forward, the McK-S flux method may enable the treatment of new problems of more complex systems that span multiple length scales. |
Monday, March 20, 2023 1:54PM - 2:06PM |
GG05.00006: Efficient and reliable scattering rate extraction for materials with complex band structures using first-principles calculations Zhen Li, Patrizio Graziosi, Neophytos Neophytou The accurate computation of the electronic transport behaviour of solid-state semiconductors is critical for the accelerated discovery and identification of candidates. Using first-principles calculations, we have developed a computationally practical approach to accurately compute scattering rate and carrier mobility, which extends existing methods for non-polar electron-phonon coupling, mainly for acoustic deformation potential scattering, to support optical deformation potential and intervalley scattering. Polar optical phonon scattering and ionized impurity scattering mechanisms are also included for materials with complex band structures. To validate our method, we compute the electronic transport properties of Mg3Sb2 and Si and compare the results with experimental measurements and more detailed scattering simulations. Compared to state-of-the-art methods, the present formalism provides competitive accuracy at about 1/40 of the overall computational cost, where the dominant part comes from extracting relevant deformation potentials from first-principles calculations. The efficiency and robustness of this approach can enable high-throughput computational studies based on accurate scattering rate and carrier mobility. |
Monday, March 20, 2023 2:06PM - 2:18PM |
GG05.00007: A mathematically-derived formula revealing the fundamental nature of the Doppler Effect, Cosmological Red-shift and Cherenkov radiation Qian Chen The well-established principle of the constancy of the velocity of light can be mathematically represented with the general equation O(to)-S(ts)=c(to-ts). Based solely on this equation without including any other assumptions, a comprehensive set of ground-breaking results was derived solely through strict mathematics, which is named “Asymmetry Theory”. |
Monday, March 20, 2023 2:18PM - 2:30PM |
GG05.00008: Small Electron Polarons Formation and Transport in Tantalum Oxynitride: Low Mobility from Hopping Migration Manoj Dey, Akash Singh, Abhishek K Singh Oxynitrides are potential photoanodes due to combinatory properties of reasonable stability, like pure oxides with a low band gap in the visible range identical to nitrides. However, low carrier mobility restricts the solar-to-hydrogen conversion efficiency from the theoretical limit. We found that polarization potential created by lattice distortion around Ta generates a driving force to trap electrons and forms small electron polarons in tantalum oxynitride (β-TaON). The localized small electron polaronic state is more favorable than the delocalized state. The donated electron from n-type single donor defects becomes self-trapped and forms a weakly bound state with the defect. The electron polarons show non-adiabatic thermally activated migration via nearest neighbor hopping. However, O substitution at bridging the N site increases the Ta–Ta hopping distance and changes the polaron hopping toward an adiabatic regime. The calculated low polaron mobility because of high migration barriers explains the experimentally observed high carrier lifetime and transport property of the β-TaON photoanode. This study provides a fundamental understanding of the charge trapping and formation of small polarons in TaON. It also prescribes a strategy to search for potential dopants to improve photocurrent generation by boosting polaron transport. |
Monday, March 20, 2023 2:30PM - 2:42PM |
GG05.00009: Sparse-rank factorization methods in quantum physics Thomas E Baker Lanczos-based algorithms have been demonstrated to play a pivotal role in quantum computing and classical methods. I review the development of these methods for a variety of physical systems and new implementations. I also review new use cases of these algorithms. |
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