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

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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. ***