Nickelate superconductivity without rare-earth magnetism: (La,Sr)NiO$_{2}$

TL;DR

This study demonstrates superconductivity in La$_{1-x}$Sr$_{x}$NiO$_{2}$ thin films without rare-earth magnetic moments, revealing a broader family of nickelates with superconducting properties and a potential self-doped superconducting state.

Contribution

It shows that (La,Sr)NiO$_{2}$ can exhibit superconductivity with optimized materials, expanding the understanding of nickelate superconductors beyond rare-earth magnetism.

Findings

Superconductivity observed in La$_{1-x}$Sr$_{x}$NiO$_{2}$ with $T_c$ up to 9 K.

Superconducting dome characterized across different lanthanides.

Indication of superconductivity in undoped LaNiO$_{2}$, suggesting self-doped states.

Abstract

The observation of superconductivity in infinite layer nickelate (Nd,Sr)NiO$_{2}$ thin films has led to rapid theoretical and experimental investigations of these copper-oxide-analogue systems [1-15]. Superconductivity has also been found in (Pr,Sr)NiO$_{2}$ [16,17], but not previously in (La,Sr)NiO$_{2}$ [2], raising a fundamental question whether superconductivity is associated with the presence of rare-earth moments [18,19]. Here we show that with significant materials optimization, substantial portions of the La$_{1-x}$Sr$_{x}$NiO$_{2}$ phase diagram can enter the regime of coherent low-temperature transport ($x$ = 0.14 - 0.20), with subsequent superconducting transitions and a maximum onset of ~ 9 K at $x$ = 0.20. Additionally, we observe the unexpected indication of a superconducting ground state in undoped LaNiO$_{2}$, which likely reflects the self-doped nature of the electronic structure. Combining the results of (La/Pr/Nd)$_{1-x}$Sr$_{x}$NiO$_{2}$ reveals a generalized superconducting dome, characterized by systematic shifts in the unit cell volume and in the relative electron-hole populations across the lanthanides.