Superconductivity in Ruddlesden-Popper nickelates: a review of recent progress, focusing on thin films

TL;DR

This review covers recent experimental and theoretical advances in Ruddlesden-Popper nickelates, especially thin films, highlighting their potential for high-temperature superconductivity and new research opportunities.

Contribution

It provides a comprehensive overview of progress in Ruddlesden-Popper nickelates with a focus on thin films and discusses future research directions.

Findings

Superconductivity observed at Tc ~ 80 K in La3Ni2O7 under high pressure.

Ambient-pressure superconductivity achieved in ultra-thin films on strained substrates.

Strain engineering in thin films extends the experimental techniques for nickelates.

Abstract

The discovery of superconductivity with Tc ~ 80 K in the nickelate Ruddlesden-Popper bilayer La3Ni2O7 at high pressure has opened a new platform for unconventional superconductivity, followed by the subsequent observation of superconductivity in trilayer La4Ni3O10, also at high pressure. Remarkably, ambient-pressure superconductivity was also observed recently in La3Ni2O7 ultra-thin films when grown on substrates that provide compressive strain. This discovery significantly extends the type of experimental techniques that can be used in nickelates, previously limited due to the high-pressure constraint. Discussing the similarities and differences among these nickel oxides will provide new insights into understanding the mechanism of high-Tc superconductivity in correlated electron systems. In this paper, we review the experimental and theoretical progress on RuddlesdenPopper nickelates, with emphasis on thin films, and discuss future perspectives and research directions.