Superconductivity in infinite-layer nickelate La$_{1-x}$Ca$_x$NiO$_2$ thin films

TL;DR

This study reports the discovery of superconductivity in La$_{1-x}$Ca$_x$NiO$_2$ thin films, revealing a superconducting dome and unique electronic properties that differ from other nickelates, highlighting the importance of lattice correlations.

Contribution

First observation of superconductivity in La$_{1-x}$Ca$_x$NiO$_2$ thin films and construction of their phase diagram, revealing distinct electronic behavior compared to Nd- and Pr-based nickelates.

Findings

Superconductivity observed at 0.15<x<0.3 doping levels.

Insulating behavior in undoped and underdoped films from 300 K to 2 K.

Sign change in Hall coefficient at low temperature for higher doping levels.

Abstract

We report the observation of superconductivity in infinite-layer Ca-doped LaNiO$_2$ (La$_{1-x}$Ca$_x$NiO$_2$) thin films and construct their phase diagram. Unlike the metal-insulator transition in Nd- and Pr-based nickelates, the undoped and underdoped La1-xCaxNiO2 thin films are entirely insulating from 300 K down to 2 K. A superconducting dome is observed at 0.15<x<0.3 with weakly insulating behavior at the overdoped regime. Moreover, the sign of the Hall coefficient $R_H$ changes at low temperature for samples with a higher doping level. However, distinct from the Nd- and Pr-based nickelates, the $R_H$-sign-change temperature remains at around 35 K as the doping increases, which begs further theoretical and experimental investigation in order to reveal the role of the 4f orbital to the (multi)band nature of the superconducting nickelates. Our results also emphasize the significant role of lattice correlation on the multiband structures of the infinite-layer nickelates.