Large spontaneous spin-splitting and enhanced effective g-factor in two-dimensional electron gases at In_0.75Ga_0.25As/In_0.75Al_0.25As metamorphic heterojunctions

We have estimated spin-splitting energy of two-dimensional electron gases formed at metamorphic In_0.75Ga_0.25As/In_0.75Al_0.25As heterojunctions by analyzing magneto-resistance traces up to 10T. This heterojunction often reveals a large spontaneous spin-splitting at low fields, while at high fields, Zeeman splitting becomes dominant. We have investigated and compared the two sanples; one reveals beating oscillation and hence has a spontaneous or zero-field spin-splitting and another does not. In the former sample, if we assume the equal sign for both the spin-splittings, the dependency of the absolute splitting energy on the magnetic field is found to have a minimum (Δ = 2meV) at about 3.5 T, in which we also confirmed a zero-field spin-splitting of Δ₀ = 11.04 meV and very much enhanced g* = -42.0 at 1.5 T. In contrast, effective g-factor (g*) obtained at high fields in the latter sample is g* = -7.7 at 1.5 T, which is fairly smaller than that in the former. Origins of those features are discussed and the possibility of linear spin-splitting dependency on magnetic field is pointed out.