Two-dimensional superconductivity at the surfaces of KTaO 3 gated with ionic liquid.

The recent discovery of superconductivity at the interfaces between KTaO 3 and EuO (or LaAlO 3 ) gives birth to the second generation of oxide interface superconductors. This superconductivity exhibits a strong dependence on the surface plane of KTaO 3 , in contrast to the seminal LaAlO 3 /SrTiO 3 interface, and the superconducting transition temperature T c is enhanced by one order of magnitude. For understanding its nature, a crucial issue arises: Is the formation of oxide interfaces indispensable for the occurrence of superconductivity? Exploiting ionic liquid (IL) gating, we are successful in achieving superconductivity at KTaO 3 (111) and KTaO 3 (110) surfaces with T c up to 2.0 and 1.0 K, respectively. This oxide-IL interface superconductivity provides a clear evidence that the essential physics of KTaO 3 interface superconductivity lies in the KTaO 3 surfaces doped with electrons. Moreover, the controllability with IL technique paves the way for studying the intrinsic superconductivity in KTaO 3 .