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

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 f ₀ into two components f ₁ and f ₂ and the appearance of the low-frequency component f ₃ was observed. Our analysis shows that the components f ₁ and f ₂ are determined by the electron densities n ₁ and n ₂ in spin-orbit split subbands while the f ₃ 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 n ₁ , n ₂ 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.