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

Abstract

Narrow HgTe quantum wells are remarkable by presence of poorly conductive two-dimensional heavy hole subband (located in the local valleys) states atop of well-conductive Dirac-like light holes at the Γ point. Here we propose and employ two methods to measure the density of states for these heavy holes. The first method uses the 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 the 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.

Quantum Transport of Dirac Fermions in HgTe Gapless Quantum Wells

“…The authors attributed such anomalous behaviour to the existence of sideband holes, which may serve as reservoir and pin the Fermi level in the gap between the Landau levels of the Dirac holes. Recently heavy hole density of the states has been measured by the capacitance technique [32].…”