Large spontaneous spin splitting in gate-controlled two-dimensional electron gases at normal In_<0.75>Ga_<0.25>As/In_<0.75>Al_<0.25>As heterojunctions

Amounts of spontaneous spin splittings were estimated from low-temperature magnetoresistances in two-dimensional electron gases created at In_Ga_As/In_Al_As heterojunctions under a gate bias. Typical sheet electron densities and mobilities in the raw wafers were ～1.0×10^/cm^2 and 2-5×10^5 cm^2/V s at 1.5 K, respectively. A maximum spin-orbit coupling constant α_ of ～30(×10^ eV m) was obtained for the van der Pauw sample. In gated Hall-bar samples, a decrease in the α_ value with decreasing gate voltage (V_g) was first confirmed in a normal heterojunction. The main origin for such a large α_, 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