Two-Dimensional Superconductivity at the CaZrO₃/KTaO₃(001) Heterointerfaces.

Abstract

Two-dimensional superconductivity at KTaO₃ (KTO) heterointerfaces has sparked intensive investigations since its discovery, yet whether the (001)-oriented KTO interface hosts superconductivity remains to be elucidated. Here, we provide unambiguous evidence of superconductivity in two-dimensional electron gases (2DEGs) at CaZrO₃/KTO(001) heterointerfaces, with a superconducting transition <i>T</i>_C up to ∼0.25 K. Notably, <i>T</i>_C increases linearly with carrier density <i>n</i>_S over the range of 4.5 × 10¹³-10.3 × 10¹³ cm^-2. Furthermore, superconductivity exhibits a pronounced dependence on crystallographic orientation, with <i>T</i>_C rising from 0.25 K for (001) to 1.04 K for (110) and 2.22 K for (111), underscoring the crucial role of interfacial symmetry in the CaZrO₃/KTO system. The two-dimensional nature of the superconducting state is corroborated by the Berezinskii-Kosterlitz-Thouless (BKT) transition and the large anisotropy of the upper critical field. For the CaZrO₃/KTO(001) sample with <i>n</i>_S = 7.7 × 10¹³ cm^-2, the estimated Ginzburg-Landau coherence length ξ_GL = 146.4 nm is larger than the superconducting layer thickness <i>d</i>_SC = 10.1 nm by a factor of ∼14.5, confirming the significant two-dimensional confinement of the CaZrO₃/KTO(001) superconductor. In addition, we demonstrate that the two-dimensional superconductivity at the CaZrO₃/KTO(001) interface can be effectively tuned by applying a back gate voltage. Our findings reveal the existence of two-dimensional superconductivity at CaZrO₃/KTO(001), providing a new platform for exploring two-dimensional superconductivity at oxide interfaces.