High-density, high-mobility ultrathin spin-polarized two-dimensional electron gas at the polar/polar LaVO$_3$/KTaO$_3$ interface: Insights from first-principles calculations

Abstract

The emergence of high-mobility two-dimensional electron gases (2DEGs) at oxide interfaces provides a fertile platform for exploring emergent quantum phenomena and next-generation oxide electronics. Here, using first-principles density functional theory (DFT) calculations, we investigate the microscopic origin of the 2DEG formed at the interface between the band insulator KTaO$_3$ (KTO) and the Mott insulator LaVO$_3$ (LVO). Although both constituents are insulating in bulk, the LVO/KTO heterostructure develops robust metallicity at the interface, consistent with experimental observations. Our calculations show that this metallic state originates from an electronic reconstruction driven by the polar discontinuity across the interface. To avoid the polar catastrophe on both the polar LVO film and the polar KTO substrate, electrons are transferred from the outer surfaces toward the interface, leading to hole accumulation in the surface VO$_2$ layer and electron accumulation in the interfacial TaO$_2$ layer. This charge redistribution stabilizes a highly confined and spin-polarized 2DEG localized at the interface. The electronic states forming the 2DEG are predominantly derived from interfacial Ta $5d_{xy}$ orbitals, confining carrier motion to the interfacial plane. Remarkably, the spin-up parabolic band hosting the 2DEG exhibits an exceptionally small effective mass, substantially lower than that of the prototypical LaAlO$_3$/SrTiO$_3$ interface, indicating the potential for enhanced carrier mobility. Furthermore, the calculated interfacial electron density is nearly an order of magnitude larger than that of LaAlO$_3$/SrTiO$_3$, consistent with experiment. These findings identify the LVO/KTO heterostructure as a promising platform for realizing high-density, high-mobility spin-polarized 2DEGs and for engineering correlated oxide interfaces for quantum electronic applications.