Stoichiometric control of 2D superconductivity and mobility at SrTiO₃-based interfaces

SrTiO₃-based conducting interfaces, that exhibit coexistence of gate tunable multi-orbital 2D superconductivity and strong Rashba spin-orbit coupling (RSOC), have ingredients to generate topological superconducting electronics for quantum application. However, the common challenge is to control the superconducting critical temperature (T_c) and electronic mobilities (μ) that are sensitive in 2D from defects, imperfections, cation stoichiometry, etc. originating from non-trivial synthesis process and limits the device dimension from its characteristic length. Besides, the origin conductivity and superconductivity are still debated, the numerous studies on LaAlO₃/SrTiO₃ interfaces suggest that superconducting condensate only forms in extreme dirty limit and suppresses strongly at low electrostatic doping below Lifshitz transition. Here we report that a small variation of Lanthanum (La) and Aluminum (Al) ratio in Al-rich LaAlO₃, as identified in XPS and STEM-EELS measurements, provides an excellent degree of freedom, not yet explored, to fine-tune systematically carrier density, mobility, and strikingly formation of superconducting condensate as well. Gate tunable superconducting phase diagram display even growing T_c below Lifshitz transition attributed to the observed larger electronic mobility which is comparable to superconducting coherence length. Our result paves the way to understand the origin of superconductivity subtler way and form devices with moderate dimensions for topological superconducting electronics.