Excited state dynamics in solid state systems investigated by ultrafast spectroscopies in the visible and terahertz regimes
Date
2022
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Publisher
University of Delaware
Abstract
Ultrafast spectroscopies on the femtosecond timescale are well suited to study electronic dynamics and coupling between quasiparticles in condensed matter systems. These interactions are of great fundamental importance and have widespread applications in engineering. Future developments in spintronics, valleytronics, and optoelectronics depend on an understanding of the couplings of electrons, phonons, magnons, and plasmons. Quasiparticle interactions take place on ultrafast timescales and can be investigated at visible and far infrared wavelengths. This work describes the development and application of time- and frequency-resolved spectroscopies to several important systems, with the purpose of directly detecting the specific quasiparticles involved in the dynamics and determining the timescales of their interactions. First, transient absorption spectroscopy and pump-degenerate four-wave mixing are utilized together to observe the electron-phonon and phonon-phonon scattering in transition metal dichalcogenides. These two spectroscopies jointly identify the specific phonons involved in these interactions. The application of pump-dlegenerate four-wave mixing to a solid state material is novel and requires an in-depth discussion of the interpretation of the measurement. Second, a time-resolved and time-domain terahertz spectroscopy instrument is developed. The characterization of the system is provided and two individual studies show its capabilities. Magnon excitations in single crystal NiO are first measured with terahertz absorption spectroscopy. The determination of these magnon frequencies demonstrates the high frequency resolution of the instrument. Following the magnon study, the charge carrier lifetimes in GaAs and ErAs:GaAs heterostructures are measured with optical pump-terahertz probe spectroscopy. The instrumentation and models of the ultrafast dynamics provide a framework for studying quasiparticle interactions in solid state systems with these techniques.
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Keywords
Electronic dynamics, Ultrafast spectroscopies, Nonlinear optics