Infinite-Layer Nickelate Superconductors: A Current Experimental Perspective of the Crystal and Electronic Structures

L E Chow,A Ariando

doi:10.3389/fphy.2022.834658

Abstract

After the reward of more than 2 decades of pursuit on the high-Tc cuprate analog with the hope to obtain a better understanding of the mechanism of high-Tc superconductivity, the discovery of superconductivity in the infinite-layer nickelate brings more mystery to the picture than expected. Tops in the list of questions are perhaps 1) absence of superconductivity in the bulk nickelate and limited thickness of the infinite-layer phase in thin film, 2) absence of superconductivity in the La-nickelate despite it being the earliest studied rare-earth nickelate, and the role of 4 f orbital in the recipe of superconductivity, 3) absence of Meissner effect and suspect of the origin of superconductivity from the interface, 4) whether nickelate hosts similar pairing symmetry to the single-band high-Tc cuprates or multiband iron-based superconductor. In this perspective article, we will discuss the following aspects: 1) stabilization of the infinite-layer phase on the SrTiO3(001) substrate and the thickness dependency of observables; 2) rare-earth dependence of the superconducting dome and phase diagram of the (La/Pr/Nd)- infinite-layer nickelate thin film; 3) experimental aspects of the measurement of Meissner effect; 4) theoretical framework and experimental study of the pairing symmetry of infinite-layer nickelate superconductor.

Highlights

Unlike cuprate, which was first synthesized in the bulk form, superconducting nickelate was only realized recently in the thin-film form [14–21], with Ni1+ in the Infinite-Layer Nickelate: Experimental Perspective infinite-layer phase that can be achieved through topotactic reduction from the perovskite compound
In addition to the bulk nickelate not being reported to show superconductivity, concrete evidence of the Meissner effect in the superconducting nickelate thin film was missing [14], leading to the suspect whether the phenomenon was interfacial in nature
High-Tc cuprate is uniquely identified with a dominant dx2−y2 -wave gap which is believed to be mediated by the antiferromagnetic superexchange interaction, that poses as a crucial factor in the high-Tc superconductivity [3]

Summary

Introduction

Around 4 decades ago, the witness of superconductivity above 30 K redefined preexisting knowledge on the mechanism of superconductivity and restructured the landscape of the playground on superconductor materials [1, 2]. We will discuss the following aspects: 1) stabilization of the infinite-layer phase on the SrTiO3(001) substrate and the thickness dependency of observables; 2) rare-earth dependence of the superconducting dome and phase diagram of the (La/Pr/Nd)- infinite-layer nickelate thin film; 3) experimental aspects of the measurement of Meissner effect; 4) theoretical framework and experimental study of the pairing symmetry of infinite-layer nickelate superconductor.

Results

Conclusion