Strongly enhanced Rashba splittings in an oxide heterostructure: A tantalate monolayer onBaHfO3

In the two-dimensional electron gas emerging at the transition metal oxide surface and interface, various exotic electronic ordering and topological phases can become experimentally more accessible with the stronger Rashba spin-orbit interaction. Here, we present a promising route to realize significant Rashba-type band splitting using a thin film heterostructure. Based on first-principles methods and analytic model analyses, a tantalate monolayer on ${\mathrm{BaHfO}}₃$ is shown to host two-dimensional bands originating from Ta ${t}_2g$ states with strong Rashba spin splittings, nearly 10% of the bandwidth, at both the band minima and saddle points. An important factor in this enhanced splitting is the significant ${t}_2g\ensuremath{-}{e}_g$ interband coupling, which can generically arise when the inversion symmetry is maximally broken due to the strong confinement of the 2DEG on a transition metal oxide surface. Our results could be useful in realizing topological superconductivity at oxide surfaces.