Heterostructures*

Emergent metallic behavior at the interface of the Mott insulator LaTiO₃ and the band insulator SrTiO₃ has been explained in terms of charge redistribution at the interface combined with strain-induced electronic structure modification. We have studied ultra thin (3 unit cells) films of LaTiO₃ and found evidence for a giant Rashba effect from quantum oscillations with an associated Berry phase, weak antilocalization in the magnetoresistance, and anisotropic in-plane magnetoresistance. In order to tune these properties, we have electrically back-gated these films. We have found a transition from a nonlinear to a linear Hall effect, a change in sign of the magnetoresistance, and, most interestingly, a peak in the zero field resistance. Based on density functional theory calculations, we attribute the nonlinear to linear Hall effect transition to an emptying of a d_xz+yz band. The peak is attributed to tuning the Fermi energy across a Rashba effect induced Dirac point.