Anisotropic electronic transport and Rashba effect of the two-dimensional electron system in (110) SrTiO₃-based heterostructures

The two-dimensional electron system in (110)Al$_2$O$_{3-\delta}$/SrTiO$_3$ heterostructures displays anisotropic electronic transport. Largest and lowest conductivity and electron mobility $\mu$ are observed along the $[001]$ and $[1\bar{1}0]$ direction, respectively. The anisotropy of the sheet resistance and $\mu$ likewise leads to a distinct anisotropic normal magnetotransport (MR) for T < 30K. However, at temperatures T<5K and magnetic field B<2T MR is dominated by weak antilocalization.Despite the rather strong anisotropy of the Fermi surfaces, the in-plane anisotropic magnetoresistance (AMR) displays two-fold non-crystalline anisotropy. However, the AMR-amplitude is found to be anisotropic with respect to the current direction, leading to a 60% larger AMR amplitude for current I along the $[001]$ direction compared to I parallel to $[1\bar{1}0]$. Tight binding calulations evidence an anisotropic Rashba-induced band splitting with dominant linear k-dependence. In combination with semiclassical Boltzmann theory the non-crystalline AMR is well described, despite the anisotropic Fermi surface.