Preparation and optimization of high-temperature superconducting Ruddlesden-Popper nickelate thin films

TL;DR

This paper presents a systematic method for growing high-quality, phase-pure Ln3Ni2O7 superconducting thin films using atomic-layer epitaxy under oxidative conditions, achieving a Tc,onset of 50 K and elucidating key growth factors.

Contribution

It introduces a controlled growth protocol for Ruddlesden-Popper nickelate films, enabling superconductivity at higher temperatures and providing insights into optimizing their structural and electronic properties.

Findings

Achieved superconducting Ln3Ni2O7 films with Tc,onset of 50 K.

Identified four critical factors for high-quality film growth.

Demonstrated the importance of oxygen regulation and interface control.

Abstract

The discovery of ambient-pressure nickelate high-temperature superconductivity provides a new platform for probing the underlying superconducting mechanisms. However, the thermodynamic metastability of Ruddlesden-Popper nickelates Lnn+1NinO3n+1 (Ln = lanthanide) presents significant challenges in achieving precise control over their structure and oxygen stoichiometry. This study establishes a systematic approach for growing phase-pure, high-quality Ln3Ni2O7 thin films on LaAlO3 and SrLaAlO4 substrates using gigantic-oxidative atomic-layer-by-layer epitaxy. The films grown under an ultrastrong oxidizing ozone atmosphere are superconducting without further post annealing. Specifically, the optimal Ln3Ni2O7/SrLaAlO4 superconducting film exhibits an onset transition temperature (Tc,onset) of 50 K. Four critical factors governing the crystalline quality and superconducting properties of Ln3Ni2O7 films are identified: 1) precise cation stoichiometric control suppresses secondary phase formation; 2) complete atomic layer-by-layer coverage coupled with 3) optimized interface reconstruction minimizes stacking faults; 4) accurate oxygen content regulation is essential for achieving a single superconducting transition and high Tc,onset. These findings provide valuable insights for the layer-by-layer epitaxy growth of diverse oxide high-temperature superconducting films.