Shear-stress-constrained superconductivity in Ruddlesden-Popper nickelates

TL;DR

This paper proposes that shear stress within a specific deformation window enables superconductivity in Ruddlesden-Popper nickelates, unifying various experimental observations.

Contribution

It introduces a shear-stress-constrained framework explaining superconductivity dependence on stress, pressure, and sample conditions in nickelates.

Findings

Superconductivity occurs only within a bounded shear-strain window.

Shear deformation influences octahedral rotations and orbital coupling.

The model explains pressure thresholds and inhomogeneity in experiments.

Abstract

Ruddlesden-Popper nickelates exhibit superconductivity under pressure in bulk crystals and under epitaxial constraint in thin films, while remaining highly sensitive to sample quality, oxygen content, defects, and stress conditions. We propose that the metastable RP lattice becomes superconducting only when the local constrained deformation of the Ni-O framework falls within a bounded shear-strain window. This deformation controls octahedral rotations, the interlayer Ni-O-Ni bond angle, and coupling between Ni dz2 and dx2-y2 orbitals. This shear-stress-constrained superconductivity scenario unifies the understanding of the pressure threshold, reversibility, spatial inhomogeneity, pressure-medium dependence, film-substrate sensitivity, and reproducibility.