Density dependent exciton dynamics and L valley anisotropy in germanium

TL;DR

This study uses optical pump-THz probe spectroscopy to explore how exciton formation in germanium depends on density and reveals anisotropic properties of electrons in the L valley, showing delayed formation and acceleration at higher densities.

Contribution

It provides new insights into exciton dynamics and L valley anisotropy in germanium through combined experimental and microscopic theoretical analysis.

Findings

Exciton formation is delayed and accelerates with increased excitation density.

Two distinct THz resonances are attributed to L valley electron anisotropy.

Spectral analysis reveals density-dependent exciton dynamics in germanium.

Abstract

Optical pump-THz probe spectroscopy is used to investigate the exciton formation dynamics and its intensity dependence in bulk Ge. Associated with the intra-excitonic 1s-2p transition, the gradual build-up of an absorption peak around 3.1 meV (0.75 THz) signifies the delayed exciton formation after optical pump which is accelerated for higher excitation densities. Analyzing the spectral shape of this THz absorption resonance, two distinct resonances are found which are attributed to the mass-anisotropy of L valley electrons via a microscopic theory.