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

TL;DR

This study provides clear evidence of two-dimensional superconductivity at CaZrO3/KTaO3 (001) heterointerfaces, with properties influenced by crystallographic orientation, carrier density, and gate voltage, highlighting the role of interfacial symmetry.

Contribution

First demonstration of 2D superconductivity at CaZrO3/KTaO3 (001) heterointerfaces, revealing orientation-dependent TC and tunability via gating.

Findings

Superconductivity observed up to TC ~0.25 K at CaZrO3/KTaO3 (001) interfaces.

TC increases linearly with carrier density from 4.5*10^13 to 10.3*10^13 cm^-2.

Superconductivity exhibits orientation dependence, with higher TC on (110) and (111) surfaces.

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 TC up to ~0.25 K. Notably, TC increases linearly with carrier density nS over the range of 4.5*10^13~10.3*10^13 cm^-2. Furthermore, superconductivity exhibits a pronounced dependence on crystallographic orientation, with TC 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 nS=7.7*10^13 cm^-2, the estimated Ginzburg-Landau coherence length {\xi}GL=146.4 nm is larger than the superconducting layer thickness dSC=10.1 nm by a factor of ~14.5, confirming 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.