Deconvolution of Rashba and Dresselhaus spin-orbit coupling by crystal axis dependent measurements of coupled InAs/GaSb quantum wells

The Dresselhaus spin-orbit interaction is expected to perturb the quantum spin Hall phase predicted to arise within InAs/GaSb coupled quantum wells. To gain a greater understanding of this interaction, the spin-orbit coupling in two InAs/GaSb coupled quantum well samples, grown along the [001] axis, was investigated along three different in-plane crystallographic axes. By measuring the crystallographic axis dependence of the Dresselhaus spin-orbit coupling, we can deconvolute this coupling from the spin splitting arising from axis-invariant Rashba spin-orbit coupling. We find that the Dresselhaus parameter is robust against an external gate bias and small changes in growth conditions, with an associated Dresselhaus parameter of (0.20 ± 0.08) × 10⁻¹¹eV m being measured across all samples and top gate bias conditions. In addition, we show that the asymmetries associated with the coupled quantum well structure, leading to Rashba spin-orbit coupling, are likely to play a dominant role in determining the spin-orbit interaction experienced by a quantum spin Hall state as the system is tuned towards charge neutrality.