Anisotropic Rashba-type spin-orbit coupling of the two-dimensional electron system in (110) SrTiO${}_3$-based heterostructures

The two-dimensional electron system in (110) Al${}_2$O${}_{3-d}$/SrTiO${}_3$ heterostructures displays anisotropic electronic transport. Structured microbridges allow to probe 4-point resistivity along different crystallographic orientations, i.e. $[$001$]$ and $[$1-10$]$. The conductivity and electron mobility along the $[$001$]$ direction is largest, while differences in sheet carrier concentration are only minor. The measurements show anisotropic normal magnetotransport for T $<$ 30 K which is correlated to the anisotropic mobility. For temperatures below 5 K transport is dominated by Rashba-type spin orbit interaction (SOI) which displays anisotropic behavior, too. SOI is found largest along the $[$001$]$ direction.