Stoichiometric control of electrical transport properties in LaAlO₃-SrTiO₃ interfaces

SrTiO₃-based conducting interfaces, which exhibit coexistence of gate-tunable 2D superconductivity and strong Rashba spin-orbit coupling (RSOC), are candidates to host topological superconductive phases. Yet, superconductivity is usually in the dirty limit, which tends to suppress nonconventional pairing and therefore challenges these expectations. Here we report on LaAlO₃/SrTiO₃ interfaces with remarkably large mobility and mean free paths comparable to the superconducting coherence length, approaching the clean limit for superconductivity. By exploiting small variations of the La/Al chemical ratio we can fine-tune systematically the carrier density, mobility and the formation of the superconducting condensate. Interestingly, we find a region in the phase diagram where the critical temperature is not suppressed below the Lifshitz transition, at odds with predictions from Bardeen–Cooper–Schrieffer theory. These findings point out the relevance of achieving a clean-limit regime to enhance the observation of unconventional pairing mechanisms in these systems.