# Density of states measurements for heavy subband of holes in HgTe quantum wells

## TL;DR

This paper introduces two methods to measure the density of states for heavy holes in HgTe quantum wells, providing insights into their electronic properties and demonstrating techniques applicable to other 2D systems.

## Contribution

The study presents novel approaches for measuring the density of states of heavy holes in HgTe quantum wells, combining thermodynamic and oscillation-based methods.

## Key findings

- Both methods yield consistent density of states estimates.
- Heavy holes exhibit large effective masses in HgTe quantum wells.
- The techniques are applicable to other two-dimensional gated systems.

## Abstract

Valence band in narrow HgTe quantum wells contains well-conductive Dirac-like light holes at the $\Gamma$ point and poorly conductive heavy hole subband located in the local valleys. Here we propose and employ two methods to measure the density of states for these heavy holes. The first method uses a gate-recharging technique to measure thermodynamical entropy per particle. As the Fermi level is tuned with gate voltage from light to heavy subband, the entropy increases dramatically, and the value of this increase gives an estimate for the density of states. The second method determines the density of states for heavy holes indirectly from the gate voltage dependence of the period of the Shubnikov-de Haas oscillations for light holes. The results obtained by both methods are in the reasonable agreement with each other. Our approaches can be applied to measure large effective carrier masses in other two-dimensional gated systems.