Measuring terahertz (THz) conductivity on an ultrafast time scale is an excellent way to observe charge-carrier dynamics in semiconductors as a function of time after photoexcitation. However, a conductivity measurement alone cannot separate the effects of charge-carrier recombination from effective mass changes as charges cool and experience different regions of the electronic band structure. Here we present a form of time-resolved magneto-THz spectroscopy which allows us to measure cyclotron effective mass on a picosecond time scale. We demonstrate this technique by observing electron cooling in the technologically-significant narrow-bandgap semiconductor indium antimonide (InSb). A significant reduction of electron effective mass from 0.032me to 0.017me is observed in the first 200ps after injecting hot electrons. Measurement of electron effective mass in InSb as a function of photo-injected electron density agrees well with conduction band non-parabolicity predictions from ab initio calculations of the quasiparticle band structure.
@article{arxiv.2109.05241,
title = {Hot electron cooling in InSb probed by ultrafast time-resolved terahertz cyclotron resonance},
author = {Chelsea Q. Xia and Maurizio Monti and Jessica L. Boland and Laura M. Herz and James Lloyd-Hughes and Marina R. Filip and Michael B. Johnston},
journal= {arXiv preprint arXiv:2109.05241},
year = {2021}
}