Ultrafast Carrier Dynamics in Metals, Superconductors, and Spin-Polarized Semiconductors

这个理论项目将研究由超快飞秒激光在金属和超导体以及自旋极化半导体中光激发的载流子的光学和动力学特性。这项工作将为简并费米系统的超快动力学提供新的理论信息；金属中的热电子效应；半导体中的准粒子动力学；以及极化和磁性半导体中的自旋相关散射。目标是将这些系统中载流子动力学的理论理解提高到与体和量子受限半导体的理解相同的水平。这涉及到实际的能带结构和散射率以及详细的输运计算。此外，对于块状半导体，将研究非平衡系统中与多体库仑相互作用相关的动态带隙重整化。其他研究者获得的准平衡条件的结果将被扩展到包括与波矢量相关的库仑空穴项的影响；一种光激发的双组分等离子体，其中一种（电子）比另一种（空穴）轻得多；并讨论了时变非平衡分布函数对带隙重整化的影响。这使我们有机会探索可观察的、时变的、非平衡的多体效应。可调谐飞秒激光器现在使详细研究固态系统中的电子过程成为可能。虽然许多最初的工作集中在体半导体和量子限制半导体上，但本研究将研究各种新系统。特别要研究的系统包括金属、超导体和极化半导体。近年来，固体系统的超快激光研究技术发展迅速，但相关的理论研究却相对滞后。这项资助将为这些系统在受到激光照射扰动时的复杂行为提供有价值的理论见解。＊＊＊

9520191 Stanton This theoretical project will investigate the optical and dynamical properties of carriers photoexcited by ultrafast, femtosecond lasers in metals and superconductors and in spin- polarized semiconductors. This work will provide new theoretical information on ultrafast dynamics in degenerate Fermi systems; hot electron effects in metals; quasi- particle dynamics in semiconductors; and, spin dependent scattering in polarized and magnetic semiconductors. The goal is to bring the theoretical understanding of the carrier dynamics in these systems up to the same level as the understanding in bulk and quantum confined semiconductors. This involves realistic band stucture and scattering rates together with detailed transport calculations. In addition, for bulk semiconductors, the dynamical band gap renormalization associated with the many-body Coulomb interaction in nonequilibrium systems will be studied. Results obtained by other investigators for quasi- equilibrium conditions will be extended to include effects associated with a wave-vector-dependent Coulomb hole term; a photoexcited two-component plasma with one species (electrons) substantially lighter than the other (holes); and, the effect of time-dependent, nonequilibrium distribution functions on the band gap renormalization. This gives us an opportunity to explore observable, time- dependent, nonequilibrium many-body effects. %%% Tunable femtosecond lasers now make possible the detailed study of electronic processes in solid state systems. While much initial work has focused on bulk semiconductors nad quantum confined semiconductors, a variety of new systems will be studied in this research. In particular, systems to be studied include metals, superconductors and polarized semiconductors. While the technology of ultrafast laser studies of solid state systems has advanced rapidly over the past few years, the associated theoretical studies have lagged. This grant will provide valu able theoretical insight on the complex behavior of these systems when perturbed by laser irradiation. ***