2D THz spectroscopic investigation of ballistic conduction-band electron dynamics in InSb

TL;DR

This study employs 2D THz spectroscopy and simulations to observe and analyze the ballistic motion and nonlinear electron dynamics in InSb, revealing anisotropic band curvature effects near the Gamma-point.

Contribution

It introduces a novel application of 2D THz spectroscopy combined with simulations to investigate ultrafast electron dynamics and band structure anisotropy in InSb.

Findings

Ballistic electron motion dominates the initial picoseconds.

Distinct spectral features relate to plasma-edge and vibrational frequencies.

Anisotropy in band curvature near the Gamma-point is observed.

Abstract

Using reflective cross-polarized 2D THz time-domain spectroscopy in the range of 1-12 THz, we follow the trajectory of the out-of-equilibrium electron population in the low-bandgap semiconductor InSb. The 2D THz spectra show a set of distinct features at combinations of the plasma-edge and vibration frequencies. Using finite difference time domain simulations combined with a tight binding model of the band structure, we assign these features to electronic nonlinearities and show that the nonlinear response in the first picoseconds is dominated by coherent ballistic motion of the electrons. We demonstrate that this technique can be used to investigate the landscape of the band curvature near the Gamma-point as illustrated by the observation of anisotropy in the (100)-plane.