  Tunable spin-orbit interaction (SOI) is an important feature for future
spin-based devices. In the presence of a magnetic field, SOI induces an
asymmetry in the energy bands, which can produce non-linear transport effects
($V\sim I^2$). Here, we focus on such effects to study the role of SOI in the
(111) LaTiO$_3$/SrTiO$_3$ interface. This system is a convenient platform for
understanding the role of SOI since it exhibits a single-band Hall-response
through the entire gate-voltage range studied. We report a pronounced rise in
the non-linear resistance at a critical in-plane field $H_{cr}$. This rise
disappears with a small out-of-plane field. We explain these results by
considering the location of the Dirac point formed at the crossing of the
spin-split energy bands. An in-plane magnetic field pushes this point outside
of the Fermi surface, and consequently changes the symmetry of the Fermi
contours and intensifies the non-linear transport. An out-of-plane magnetic
field opens a gap at the Dirac point, thereby significantly diminishing the
non-linear effects. We propose that magnetoresistance effects previously
reported in interfaces with SOI could be comprehended within our suggested
scenario.
