Terahertz Quantum Hall Effect in a Topological Insulator

TL;DR

This study uses THz spectroscopy to explore the charge dynamics and quantum Hall effect in a topological insulator, revealing Dirac carriers and resonant oscillations at THz frequencies.

Contribution

It provides the first comprehensive characterization of charge carriers and observes quantum Hall oscillations at THz frequencies in a topological insulator.

Findings

Fermi velocity confirms Dirac nature of carriers

Quantum Hall oscillations observed at THz frequencies

Surface state density matches transport measurements

Abstract

Using THz spectroscopy in external magnetic fields we investigate the low-temperature charge dynamics of strained HgTe, a three dimensional topological insulator. From the Faraday rotation angle and ellipticity a complete characterization of the charge carriers is obtained, including the 2D density, the scattering rate and the Fermi velocity. The obtained value of the Fermi velocity provides further evidence for the Dirac character of the carriers in the sample. In resonator experiments, we observe quantum Hall oscillations at THz frequencies. The 2D density estimated from the period of these oscillations agrees well with direct transport experiments on the topological surface state. Our findings open new avenues for the studies of the finite-frequency quantum Hall effect in topological insulators.