Observation of perfect diamagnetism and interfacial effect on the electronic structures in Nd0.8Sr0.2NiO2 superconducting infinite layers

TL;DR

This study demonstrates perfect diamagnetism in Nd0.8Sr0.2NiO2 thin films, revealing interface and strain effects on their electronic and magnetic properties, and highlights thickness-dependent band structure modifications related to superconductivity.

Contribution

It provides direct evidence of superconductivity through perfect diamagnetism and elucidates the role of interface, strain, and thickness in shaping the electronic structure of nickelate thin films.

Findings

Perfect diamagnetism confirms superconductivity in Nd0.8Sr0.2NiO2 films.

Thickness influences the Hall-coefficient and electronic band structure.

Interface and strain effects induce a dominant electron-like band in ultrathin films.

Abstract

Nickel-based complex oxides have served as a playground for decades in the quest for a copper-oxide analog of the high-temperature superconductivity. They may provide clues towards understanding the mechanism and an alternative route for high-temperature superconductors. The recent discovery of superconductivity in the infinite-layer nickelate thin films has fulfilled this pursuit. However, material synthesis remains challenging, direct demonstration of perfect diamagnetism is still missing, and understanding of the role of the interface and bulk to the superconducting properties is still lacking. Here, we show high-quality Nd0.8Sr0.2NiO2 thin films with different thicknesses and demonstrate the interface and strain effects on the electrical, magnetic and optical properties. Perfect diamagnetism is achieved, confirming the occurrence of superconductivity in the films. Unlike the thick films in which the normal-state Hall-coefficient changes signs as the temperature decreases, the Hall-coefficient of films thinner than 5.5 nm remains negative, suggesting a thickness-driven band structure modification. Moreover, X-ray absorption spectroscopy reveals the Ni-O hybridization nature in doped infinite-layer nickelates, and the hybridization is enhanced as the thickness decreases. Consistent with band structure calculations on the nickelate/SrTiO3 heterostructure, the interface and strain effect induce a dominating electron-like band in the ultrathin film, thus causing the sign-change of the Hall-coefficient.