Coexistence of ferromagnetism and superconductivity at KTaO$_3$ heterointerfaces

TL;DR

This paper reports the discovery of coexistence of superconductivity and ferromagnetism at KTaO$_3$ heterointerfaces, revealing long-range ferromagnetic order and its origin, which advances understanding of their interplay in complex oxides.

Contribution

It provides the first experimental evidence of long-range ferromagnetism coexisting with superconductivity at KTaO$_3$ heterointerfaces, with insights into its origin from oxygen vacancies.

Findings

Observation of in-plane ferromagnetic order above room temperature

Identification of oxygen vacancies as the source of ferromagnetism

Evidence of time-reversal symmetry breaking superconductivity

Abstract

The coexistence of superconductivity and ferromagnetism is a long-standing issue in superconductivity due to the antagonistic nature of these two ordered states. Experimentally identifying and characterizing novel heterointerface superconductors that coexist with magnetism presents significant challenges. Here, we report the experimental observation of two-dimensional long-range ferromagnetic order in the KTaO$_3$ heterointerface superconductor, showing the coexistence of superconductivity and ferromagnetism. Remarkably, our direct current superconducting quantum interference device measurements reveal an in-plane magnetization hysteresis loop persisting above room temperature. Moreover, the first-principles calculations and X-ray magnetic circular dichroism measurements provide decisive insights into the origin of the observed robust ferromagnetism, attributing it to oxygen vacancies that localize electrons in nearby Ta 5$d$ states. Our findings not only suggest KTaO$_3$ heterointerfaces as time-reversal symmetry breaking superconductors, but also inject fresh momentum into the exploration of the intricate interplay between superconductivity and magnetism, enhanced by the strong spin-orbit coupling inherent to the heavy Ta in 5$d$ orbitals of KTaO$_3$ heterointerfaces.