Download or read book Nonlinear Terahertz Interactions in Two Dimensional Systems written by Sayyed Hadi Razavi-Pour and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Reducing the dimensionality of a material from 3D to 2D introduces new quantum effects that can be exploited to see new physics and produce new devices. Two examples of such materials are graphene, a single layer of carbon atoms, and quantum well heterostructures confining charges to a planar potential well. A powerful method for observing charge transport in these 2D materials is time-resolved terahertz (THz) spectroscopy, using picosecond pulses of far-infrared light to measure the complex valued ac conductivity. In this thesis, THz spectroscopy is used to study the linear and nonlinear electrodynamic response of two 2D systems: graphene and self-assembled metal halide perovskite quantum wells. In graphene, THz field-induced bleaching is studied, found to be well described by simple phenomenological reduction in intraband absorption using a free carrier Drude model that includes neutral and charged impurity scattering as well as optical phonon scattering. The Fermi level dependence of this nonlinearity is studied for the first time, which allows us to separate the contributions of long and short range momentum scattering and map their dependence on the field amplitude. We find, contrary to previous work, that the increase in scattering cannot be explained by an increase in the lattice temperature alone and that other mechanisms such as carrier-carrier scattering must be accounted for to explain the effect. Our results provide a deeper understanding of transport in graphene devices operating at THz frequencies and in modest kV/cm field strengths present in most devices. Second, time-resolved multi-THz spectroscopy was used to investigate carrier dynamics in 2D organic metallic halide perovskite (OMHP) systems. The 2D OMHPs are promising photovoltaic materials showing reduced sensitivity to environmental degradation, however their photoconductivity response has been unexplored on ultrafast time scales. We observed a rapid decay of injected photocarriers on a 10-100 ps time scale, indicating a significant trap/decay channel that limits device performance. Supporting hyperspectral photoluminescent imaging measurements confirm the band gap shift of the naturally formed quantum wells, however also show significant surface structural defects serving as monomolecular traps. We show how mono-molecular, bimolecular and Auger constants are sensitive to the changes in the electronic confinement of the quantum wells, of importance to devices attempting to exploit their tunable optical properties and environmental stability." --