Superconductivity forms out of the condensation of Cooper pairs of electrons. The mechanism by which Cooper pairs are created in non-conventional superconductors is often elusive because experimental signatures that connect a specific pairing mechanism to the properties of superconducting state are rare. The recently discovered superconducting oxide-insulator/KTaO3 interface may offer clues about its origins. Here we observe distinct dependences of the superconducting transition temperature Tc on carrier density n2D for electron gases formed at KTaO3 (111), (001) and (110) interfaces. For the KTaO3 (111) interface, a remarkable linear dependence of Tc on n2D is observed over a range of nearly one order of magnitude. Further, our study of the dependence of superconductivity on gate electric fields reveals the role of the interface in mediating superconductivity, which also allows for a reversible electric switching of superconductivity at T = 2 K. We found that the extreme sensitivity of superconductivity to crystallographic orientation can be explained by Cooper pairing via inter-orbital interactions induced by the inversion-breaking transverse optical (TO1) phonons and quantum confinement. This mechanism is also consistent with the dependence of Tc on n2D at the KTaO3 (111) interface. Our study may shed light on the pairing mechanism in other superconducting quantum-paraelectrics.
@article{arxiv.2203.05867,
title = {Tunable superconductivity at the oxide-insulator/KTaO$_3$ interface and its origin},
author = {Changjiang Liu and Xianjing Zhou and Deshun Hong and Brandon Fisher and Hong Zheng and John Pearson and Dafei Jin and Michael R Norman and Anand Bhattacharya},
journal= {arXiv preprint arXiv:2203.05867},
year = {2023}
}