Spin-orbit splitting of the conduction band in HgTe quantum wells: Role of different mechanisms

Abstract

Spin-orbit splitting of conduction band in HgTe quantum wells was studied experimentally. In order to recognize the role of different mechanisms, we carried out detailed measurements of the Shubnikov-de Haas oscillations in gated structures with a quantum well widths from 8 to 18 nm over a wide range of electron density. With increasing electron density controlled by the gate voltage, splitting of the maximum of the oscillation Fourier spectrum f0 into two components f1 and f2 and the appearance of the low-frequency component f3 was observed. Our analysis shows that the components f1 and f2 are determined by the electron densities n1 and n2 in spin-orbit split subbands while the f3 component results from magneto-intersubband oscillations so that it is determined by the difference between these densities Δn. This allows us to obtain all three values n1, n2 and Δn independently. Comparison of the data obtained with results of self-consistent calculations carried out within the framework of four-band kP model shows that the main contribution to spin-orbit splitting comes from the Bychkov-Rashba effect. Contribution of the interface inversion asymmetry to the splitting of the conduction band turns out to be four-to-five times less than that for the valence band in the same structures.