Tunable electron-electron interactions in LaAlO₃/SrTiO₃ nanostructures

The interface between the two complex oxides LaAlO₃ and SrTiO₃ has remarkable properties that can be locally reconfigured between conducting and insulating states using a conductive atomic force microscope. Prior investigations of "sketched" quantum dot devices revealed a phase in which electrons form pairs,
implying a strongly attractive electron-electron interaction. Here, we show that these devices with strong electron-electron interactions can exhibit a gate-tunable transition from a pair-tunneling regime to a single-electron (Andreev bound state) tunneling regime where the interactions become repulsive. The electron-electron interaction sign change is associated with a Lifshitz transition where the d_xz and d_yz bands start to become occupied. This electronically tunable electron-electron interaction, combined with the nanoscale
reconfigurability of this system, provides an interesting starting point towards solid-state quantum simulation.