Large spontaneous spin splitting in gate-controlled two-dimensional electron gases at normal In_0.75Ga_0.25As/In_0.75Al_0.25As heterojunctions

Amounts of spontaneous spin splittings were estimated from low-temperature magnetoresistances in two-dimensional electron gases created at In_0.75Ga_0.25As/In_0.75Al_0.25As heterojunctions under a gate bias. Typical sheet electron densities and mobilities in the raw wafers were ∼1.0×10¹²/cm² and 2-5×10⁵ cm²/V s at 1.5 K, respectively. A maximum spin-orbit coupling constant α_zero of ∼30 (×10^-12eV m) was obtained for the van der Pauw sample. In gated Hall-bar samples, a decrease in the α_zero value with decreasing gate voltage (V_g) was first confirmed in a normal heterojunction. The main origin for such a large α_zero, which is a few times larger than any previously reported, was found to be a structure-dependent so-called interface contribution in the Rashba term.