Atomic-scale confinement of superconductivity at (111)KTaO₃ interfaces

In the search for unconventional superconducting states, various material systems have been explored, with KTaO₃-based superconductors emerging as promising candidates. Interfacial superconductivity in KTaO₃ shows a unique correlation between enhanced critical temperature and reduced symmetry at the interface, suggesting that inversion symmetry breaking is crucial for the formation of the superconducting state(1,2). Few materials exhibit such a correlation, making KTaO₃ interfaces ideal for investigating the interplay between symmetry breaking, enhanced spin-orbit coupling, and their impact on superconductivity.

We study the superconducting critical fields of 2-dimensional electron gasses at KTaO₃(111) interfaces as a function of electrostatic back-gating. Our work reveals in-plane critical fields of unprecedented magnitudes in two dimensional oxide interfaces. By comparing the critical fields in-plane and out-of-plane we discover an extremely anisotropic superconductor with an effective thickness below 1 nm and a 12-fold violation of the Chandrasekhar-Clogston paramagnetic limit. The analysis of the weak anti-localization indicates that the enhancement of the critical fields is due to an exceptionally thin superconducting layer and spin-orbit-scattering-suppressed paramagnetic susceptibility. Our research underscores the critical role of spin-orbit coupling and two-dimensional confinement in understanding superconductivity at oxide interfaces.

References:

(1). Changjiang Liu, et. al. Tunable superconductivity and its origin at KTaO3 interfaces. Nature Communications, 14(1):951, feb 2023.

(2). Maria N. Gastiasoro, et. al. Theory of superconductivity mediated by Rashba coupling in incipient ferroelectrics. Physical Review B, 105:224503, 6 2022.