Low temperature terahertz spectroscopy of n-InSb through a magnetic field driven metal-insulator transition

TL;DR

This study employs cryogenic terahertz spectroscopy with magnetic fields to investigate the metal-insulator transition in n-InSb, revealing plasma and donor transition features across the transition.

Contribution

It introduces a novel experimental setup combining fiber-coupled THz spectroscopy with high magnetic fields at cryogenic temperatures to study the MIT in n-InSb.

Findings

Observation of plasma edge and magneto-plasmon modes in the metallic state.

Detection of a broad THz band at the MIT onset.

Identification of the 1s -> 2p- transition in the insulating state.

Abstract

We use fiber-coupled photoconductive emitters and detectors to perform terahertz (THz) spectroscopy of lightly-doped n-InSb directly in the cryogenic (1.5 K) bore of a high-field superconducting magnet. We measure transmission spectra from 0.1-1.1 THz as the sample is driven through a metal-insulator transition (MIT) by applied magnetic field. In the low-field metallic state, the data directly reveal the plasma edge and magneto-plasmon modes. With increasing field, a surprisingly broad band (0.3-0.8 THz) of low transmission appears at the onset of the MIT. This band subsequently collapses and evolves into the sharp 1s -> 2p- transition of electrons `frozen' onto isolated donors in the insulating state.