Spontaneous rotational symmetry breaking in KTaO$_3$ heterointerface superconductors

TL;DR

This study reports the observation of spontaneous rotational symmetry breaking in superconductivity at the a-YAlO3/KTaO3 heterointerface, indicating an unconventional mixed-parity pairing state influenced by strong spin-orbit coupling.

Contribution

It provides experimental evidence of intrinsic rotational symmetry breaking in superconductivity at a heterointerface, revealing a mixed s- and p-wave pairing state due to spin-orbit coupling.

Findings

Twofold symmetric oscillations in magnetoresistance and critical field deep inside the superconducting state.

Anisotropy vanishes in the normal state, indicating it is intrinsic to the superconducting phase.

Suggests unconventional pairing interaction involving mixed-parity states.

Abstract

Broken symmetries play a fundamental role in superconductivity and influence many of its properties in a profound way. Understanding these symmetry breaking states is essential to elucidate the various exotic quantum behaviors in non-trivial superconductors. Here, we report an experimental observation of spontaneous rotational symmetry breaking of superconductivity at the heterointerface of amorphous (a)-YAlO$_3$/KTaO$_3$(111) with a superconducting transition temperature of 1.86 K. Both the magnetoresistance and superconducting critical field in an in-plane field manifest striking twofold symmetric oscillations deep inside the superconducting state, whereas the anisotropy vanishes in the normal state, demonstrating that it is an intrinsic property of the superconducting phase. We attribute this behavior to the mixed-parity superconducting state, which is an admixture of \emph{s}-wave and \emph{p}-wave pairing components induced by strong spin-orbit coupling inherent to inversion symmetry breaking at the heterointerface of a-YAlO$_3$/KTaO$_3$. Our work suggests an unconventional nature of the underlying pairing interaction in the KTaO$_3$ heterointerface superconductors, and brings a new broad of perspective on understanding non-trivial superconducting properties at the artificial heterointerfaces.