Strongly enhanced Rashba splitting in the perovskite tantalate-hafnate heterostructure

In addition to superconductivity and magnetism, one notable ingredient of the two-dimensional electron gas (2DEG) emerging at the transition metal oxide surface is the Rashba-Dresselhaus spin-orbit interaction, the momentum-dependent spin splitting due to the broken inversion symmetry and atomic spin-orbit coupling. However, it has not been understood how this splitting can be maximized in a physical system without applying external electric field. Here, we present a promising route to realize significant Rashba-type band splitting using thin film heterostructure. Based on a first-principles method and analytic model analysis, a tantalate layer on BaHfO$_3$ is shown to host a two-dimensional bands originating from Ta $t_{2g}$ orbitals with strongly enhanced Rashba-Dresselhaus spin splittings at both the band minima and saddle points. A significant $t_{2g}$-$e_g$ coupling that contributes to this enhanced splitting is likely to be a generic feature for the surface 2DEG of transition metal oxide with maximal inversion symmetry breaking. Our results could be important in realizing topological superconductivity and potentially useful for spintronics application.