Spin-orbit splitting of valence and conduction bands in HgTe quantum wells near the Dirac point

TL;DR

This study experimentally investigates the spin-orbit splitting in HgTe quantum wells near the Dirac point, revealing a strong valence band splitting and negligible conduction band splitting, challenging existing theoretical models.

Contribution

The paper provides the first experimental evidence of asymmetric spin-orbit splitting in HgTe quantum wells and demonstrates the importance of interface asymmetry in theoretical modeling.

Findings

Valence band strongly split by spin-orbit interaction

Conduction band splitting is negligible within experimental accuracy

Interface asymmetry explains experimental results better than symmetric models

Abstract

Energy spectra both of the conduction and valence bands of the HgTe quantum wells with a width close to the Dirac point were studied experimentally. Simultaneous analysis of the Shubnikov-de Haas oscillations and Hall effect over a wide range of electron and hole densities gives surprising result: the top of the valence band is strongly split by spin-orbit interaction while the splitting of the conduction band is absent, within experimental accuracy. Astonishingly, but such a ratio of the splitting values is observed as for structures with normal spectrum so for structures with inverted one. These results do not consistent with the results of kP calculations, in which the smooth electric filed across the quantum well is only reckoned in. It is shown that taking into account the asymmetry of the quantum well interfaces within a tight-binding method gives reasonable agreement with the experimental data.