Field re-entrant superconductivity in Eu-doped infinite-layer nickelates

TL;DR

This study reports the discovery of field-induced re-entrant superconductivity in Eu-doped infinite-layer nickelates, revealing complex magnetic interactions and expanding the understanding of unconventional superconductivity in correlated oxides.

Contribution

It demonstrates for the first time that Eu doping induces a magnetic-field-induced re-entrant superconducting phase in infinite-layer nickelates, highlighting the role of magnetism in high-temperature superconductivity.

Findings

Re-entrant superconductivity observed after suppression at low fields.

Superconducting phase remains robust across various temperatures and fields.

Unconventional behavior indicated by nonlinear Hall transport and hysteretic magnetoresistance.

Abstract

Intertwined superconducting and magnetic orders may give rise to exotic quantum phases, including field-induced and re-entrant superconductivity. However, such magnetism-enhanced superconductivity has remained elusive in superconductors with higher transition temperatures. While infinite-layer nickelates represent a new class of unconventional superconductors, the impact of rare-earth magnetism on superconducting properties remains largely unexplored. Here, we show that Eu-doped infinite-layer nickelate Sm$_{0.95-x}$Ca$_{0.05}$Eu$_x$NiO$_2$ exhibits a magnetic-field-induced re-entrant superconducting phase in the Eu-rich over-doped regime. Zero-resistance transport and high-field diamagnetic screening confirm the superconducting nature of this phase, which emerges after the initial suppression of low-field superconductivity and remains robust across a broad range of temperatures, fields and field orientations. In the same doping range, we observe nonlinear Hall transport and hysteretic magnetoresistance, indicating the unconventional nature of the re-entrant behaviour. While partially consistent with a compensation mechanism between the Eu-derived exchange field and the applied field, our data reveal pronounced deviations from this model at the highest-doping levels. Our findings establish infinite-layer nickelates as a fertile platform for exploring magnetically driven high-field superconductivity in strongly correlated oxides.