Evolution of the Superfluid Density in Infinite-Layer Nickelates

TL;DR

This study investigates how the superfluid density evolves in infinite-layer nickelates, revealing a correlation with $T_c$, the influence of Nd magnetism, and the role of phase fluctuations in superconductivity.

Contribution

It provides the first systematic measurement of superfluid density across the doping range in nickelates, highlighting the interplay between magnetism and superconductivity.

Findings

Superfluid stiffness correlates with $T_c$ approximately as its square root.

Strong coupling exists between Nd 4f moments and the superfluid.

Superconducting phase fluctuations significantly limit $T_c$.

Abstract

Nickelate superconductors provide a valuable new platform for the study of unconventional superconductivity that is complementary to the cuprates. One of the central puzzles about high-temperature superconductors is what factors determine the scale of their superconducting transition temperature ($T_\mathrm{c}$). To address this question for infinite-layer nickelates, we present a systematic mutual inductance study of the superfluid density across the doping-dependent superconducting dome of $\mathrm{Nd}_{1-x}\mathrm{Sr}_x\mathrm{NiO}_2$. We observe a weak superfluid stiffness that exhibits an approximately square-root correlation with $T_\mathrm{c}$. We also find a strong interplay between Nd magnetism and the superconducting phase, manifested as a substantial low-temperature suppression of superfluid density. These observations highlight the importance of superconducting phase fluctuations in limiting $T_\mathrm{c}$ and unexpectedly strong coupling between the Nd 4$f$ moments and the superfluid.