Amounts of spontaneous spin splittings were estimated from low-temperature magnetoresistances in two-dimensional electron gases created at In0.75Ga0.25As/In0.75Al0.25As 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 αzero of ∼30 (×10-12eV m) was obtained for the van der Pauw sample. In gated Hall-bar samples, a decrease in the αzero value with decreasing gate voltage (Vg) was first confirmed in a normal heterojunction. The main origin for such a large αzero, 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.
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