Ferromagnetic exchange, spin-orbit coupling and spiral magnetism at the LaAlO_3/SrTiO_3 interface

摘要

The electronic properties of the polar interface between insulating oxides isa subject of great current interest. An exciting new development is theobservation of robust magnetism at the interface of two non-magnetic materialsLaAlO_3 (LAO) and SrTiO_3 (STO). Here we present a microscopic theory for theformation and interaction of local moments, which depends on essential featuresof the LAO/STO interface. We show that correlation-induced moments arise due tointerfacial splitting of orbital degeneracy. We find that gate-tunable Rashbaspin-orbit coupling at the interface influences the exchange interactionmediated by conduction electrons. We predict that the zero-field ground stateis a long-wavelength spiral and show that its evolution in an external fieldaccounts semi-quantitatively for torque magnetometry data. Our theory describesqualitative aspects of the scanning SQUID measurements and makes severaltestable predictions for future experiments.