Physics of ultrathin films and heterostructures of rare earth nickelates

TL;DR

This paper reviews the complex electronic and magnetic phenomena in ultrathin rare earth nickelate films and heterostructures, highlighting recent experimental advances and future research directions in understanding their phase transitions and magnetic states.

Contribution

It provides a comprehensive overview of the current understanding and challenges in studying ultrathin rare earth nickelates, emphasizing the interplay between structure, electronic behavior, and magnetism.

Findings

Epitaxial strain and quantum confinement induce new phenomena in ultrathin nickelate films.

Interfacial charge transfer influences electronic and magnetic properties.

Future research aims to clarify the origins of metal-insulator transitions and magnetic configurations.

Abstract

The electronic structure of transition metal oxides featuring correlated electrons can be rationalized within the Zaanen-Sawatzky-Allen framework. Following a brief description of the present paradigms of electronic behavior, we focus on the physics of rare earth nickelates as an archetype of complexity emerging within the charge transfer regime. The intriguing prospect of realizing the physics of high $T_c$ cuprates through heterostructuring resulted in a massive endeavor to epitaxially stabilize these materials in ultra-thin form. A plethora of new phenomena unfolded in such artificial structures due to the effect of epitaxial strain, quantum confinement, and interfacial charge transfer. Here we review the present status of artificial rare-earth nickelates in an effort to uncover the interconnection between the electronic and magnetic behavior and the underlying crystal structure. We conclude by discussing future directions to disentangle the puzzle regarding the origin of the metal-insulator transition, the role of oxygen holes, and the true nature of the antiferromagnetic spin configuration in the ultra-thin limit.