Linear and Nonlinear Ultrafast Time Resolved Spectroscopy of Topological Insulators, Weyl Semimetals and Semiconducting Nanowires

Abstract

Ultrafast time resolved spectroscopy has recently gained immense significance due to its potential capability to explore the dynamics of photoexcited carriers in condensed matter systems. The technique has proved to be a very powerful tool in understanding the relaxation process of photogenerated carriers by providing insight into various scattering mechanisms of charge carriers, which, in turn, find significance for practical applications in optoelectronic and photonic devices. On the other hand, condensed matter physics have also witnessed a drastic change over the past few years with the introduction of topological band structure, leading to the discovery of many new materials with extraordinary properties. This has motivated the research community to investigate various scattering mechanisms of charge carriers in topological materials, both in bulk crystals as well as in nanomaterials, where the later further modifies the band structure due to confinement effects. In this work, we report our studies on understanding the carrier relaxation dynamics in topological insulators (Bi_2 Te_3,SnBi_4 Te_7), type -1 Weyl semimetals (TaAs, TaP, NbAs and NbP) and semiconducting nanowires (Te NWs) using ultrafast time resolved spectroscopy. The work mainly covers the linear and second order response of the photoexcited carriers in these materials, studied using time resolved terahertz (THz) spectroscopy and time resolved second harmonic generation (TR - SHG), respectively. The experimental results are then explained using theoretical models emphasizing on different analytical calculations for understanding the carrier relaxation dynamics, thereby giving more microscopic insight into various physical processes.