Energy spectrum of semimetallic HgTe quantum wells

TL;DR

This paper combines experimental magneto-optical spectroscopy and theoretical analysis to map the energy dispersion relations of semimetallic HgTe quantum wells, revealing detailed band structure features and demonstrating a method for direct band structure determination.

Contribution

It provides the first detailed experimental and theoretical mapping of electron and hole dispersion relations in semimetallic HgTe quantum wells using cyclotron resonance and capacitance measurements.

Findings

Good agreement between experimental data and theoretical calculations.

Identification of subtle features like band splitting and overlaps.

Demonstration of cyclotron resonance as a tool for band structure analysis.

Abstract

Quantum wells (QWs) based on mercury telluride (HgTe) thin films provide a large scale of unusual physical properties starting from an insulator via a two-dimensional Dirac semimetal to a three-dimensional topological insulator. These properties result from the dramatic change of the QW band structure with the HgTe film thickness. Although being a key property, these energy dispersion relations cannot be reflected in experiments due to the lack of appropriate tools. Here we report an experimental and theoretical study of two HgTe quantum wells with inverted energy spectrum in which two-dimensional semimetallic states are realized. Using magneto-optical spectroscopy at sub-THz frequencies we were able to obtain information about electron and hole cyclotron masses at all relevant Fermi level positions and different charge densities. The outcome is also supported by a Shubnikov-de Haas analysis of capacitance measurements, which allows obtaining information about the degeneracy of the active modes. From these data, it is possible to reconstruct electron and hole dispersion relations. Detailed comparative analysis of the energy dispersion relations with theoretical calculations demonstrates a good agreement, reflecting even several subtle features like band splitting, the second conduction band, and the overlaps between the first conduction and first valence band. Our study demonstrates that the cyclotron resonance experiments can be efficiently used to directly obtain the band structures of semimetallic 2D materials.