Two-dimensional semimetal in a wide HgTe quantum well: Magnetotransport and energy spectrum

Abstract

The results of an experimental study of the magnetoresistivity and the Hall and Shubnikov-de Haas effects for a heterostructure with a HgTe quantum well of $20.2$ nm width are reported. The measurements were performed on gated samples over a wide range of electron and hole densities including the vicinity of a charge neutrality point. Analyzing the data, we conclude that the electron and hole energy spectra are in qualitative agreement with those calculated within the framework of $kP$ model. The electron and hole subbands are overlapped due to the nonmonotonic dispersion of the hole subband resulting in a semimetallic state. The main result of the paper, however, is the drastic quantitative difference in the experimental and calculated spectra of the hole subband. So, the hole effective mass found from the analysis of the Shubnikov-de Haas oscillations is positive and equal to approximately $0.2{m}_{0}$ and practically independent of the quasimomentum ($k$) starting from ${k}^{2}\ensuremath{\simeq}0.7\ifmmode\times\else\texttimes\fi{}{10}^{12}$ cm${}^{\ensuremath{-}2}$, while the theory predicts negative (electronlike) effective mass up to ${k}^{2}\ensuremath{\simeq}6\ifmmode\times\else\texttimes\fi{}{10}^{12}$ cm${}^{\ensuremath{-}2}$. The experimental effective mass near $k=0$, where the hole energy spectrum is electronlike, is close to $\ensuremath{-}0.005{m}_{0}$, whereas the theoretical value is about $\ensuremath{-}0.1{m}_{0}$.