Superconductivity in the parent infinite-layer nickelate NdNiO$_2$

TL;DR

This study presents evidence of superconductivity up to 11 K in NdNiO$_2$ thin films, suggesting potential intrinsic superconductivity in parent infinite-layer nickelates or doping-induced effects, challenging existing phase diagrams.

Contribution

It provides the first comprehensive investigation of superconductivity in NdNiO$_2$ thin films, exploring its origins and implications for nickelate phase diagrams.

Findings

Superconductivity observed up to 11 K in NdNiO$_2$ films.

Superconductivity may be intrinsic or due to doping effects.

Disorder and doping pathways influence superconductivity.

Abstract

We report evidence for superconductivity with onset temperatures up to 11 K in thin films of the infinite-layer nickelate parent compound NdNiO$_2$. A combination of oxide molecular-beam epitaxy and atomic hydrogen reduction yields samples with high crystallinity and low residual resistivities, a substantial fraction of which exhibit superconducting transitions. We survey a large series of samples with a variety of techniques, including electrical transport, scanning transmission electron microscopy, x-ray absorption spectroscopy, and resonant inelastic x-ray scattering, to investigate the possible origins of superconductivity. We propose that superconductivity could be intrinsic to the undoped infinite-layer nickelates but suppressed by disorder due to its nodal order parameter, a finding which would necessitate a reconsideration of the nickelate phase diagram. Another possible hypothesis is that the parent materials can be hole doped from randomly dispersed apical oxygen atoms, which would suggest an alternative pathway for achieving superconductivity.