Spin-Orbit Interaction and Magnetic Order in (111) Oriented (La_0.3Sr_0.7)(Al_0.65Ta_0.35)/SrTiO₃ Heterostructures

The 2-dimensional carrier gas in (111) oriented SrTiO₃ (STO) based heterostructures has attracted a lot of attention due to its complex Fermi surface and the possibility of exotic topological physics. We present magnetoresistance (MR) studies on (111) oriented (La_0.3Sr_0.7)(Al_0.65Ta_0.35)/SrTiO₃ (LSAT/STO), which is less strained as compared to the better studied LaAlO₃/STO. We find that at high positive values of the applied gate voltage V_g, transport is dominated by high mobility electron-like carriers with a tendency towards weak localization. As V_g is lowered, carrier mobility is reduced, hole-like carriers start becoming important and weak anti-localization effects become pronounced. This indicates that spin-orbit interaction (SOI) is stronger in this regime, in contrast to what has been observed in (100) STO based structures. We have earlier reported on hysteretic MR that develops at millikelvin temperatures at low V_g,¹ signifying that low mobility carriers with strong SOI may play a role in supporting a ferromagnetic phase in this system. We believe these results can shed light on how the interplay between crystal orientation and strain can affect the properties of STO based carrier gases. [1] Bal et al, Appl. Phys. Lett. 111, 081604 (2017)