Source capture
Authors Liling Sun, Shu Cai, Jinyu Zhao, Qi Wu, Yang Ding, Tao Xiang, Ho-kwang Mao
arXiv / Publisher https://arxiv.org/abs/2605.14265
PDF https://arxiv.org/pdf/2605.14265
Relevance score 5.312
Primary category cond-mat.supr-con
Published 2026-05-15
Research paradigm Theoretical
Sample form Both

Summary

Ruddlesden-Popper nickel oxides exhibit superconductivity under both high-pressure bulk and thin-film epitaxial constraints, yet this behavior is highly dependent on sample quality, oxygen content, defects, and stress states. This paper proposes that metastable RP lattices enter the superconducting state only when the local constrained deformation of the Ni-O framework falls within a bounded shear strain window; this deformation governs octahedral rotations, interlayer Ni-O-Ni bond angles, and the coupling between Ni dz2 and dx2-y2 orbitals. This shear-stress-constrained superconductivity (SSCS) framework unifies previously observed phenomena such as pressure thresholds, reversibility, spatial inhomogeneity, pressure medium dependence, film-substrate sensitivity, and reproducibility challenges. The SSCS scenario does not replace the role of traditional factors such as bond angles, bond lengths, orbital occupancy, oxygen stoichiometry, or carrier density, but rather identifies the mechanical and symmetry conditions required for these factors to cooperatively stabilize the superconducting state. The brittleness and heterogeneity observed in nickel oxide superconductors are not extrinsic complexities but rather core diagnostic features of the superconducting state itself. This perspective provides specific experimental pathways for improving reproducibility and unifies the physical mechanisms underlying compressed bulk materials, epitaxial films, chemically substituted samples, and hybrid RP structures within a single conceptual framework.

Materials

Methods

Keywords

  • shear stress
  • metastable rp lattice
  • ni o ni bond angle
  • octahedral rotation
  • inhomogeneous superconductivity
  • reversibility
  • pressure threshold

Highlights

  • Proposes the shear-stress-constrained superconductivity (SSCS) scenario as a unified framework for RP nickelate superconductivity.
  • Identifies shear stress as a key parameter, not just hydrostatic pressure, and provides concrete experimental tests for the scenario.

Conclusions

  • Superconductivity in RP nickelates appears only when the local constrained deformation of the Ni-O framework falls within a bounded shear-strain window.
  • The shear-stress-constrained superconductivity (SSCS) scenario unifies the understanding of pressure threshold, reversibility, spatial inhomogeneity, pressure-medium dependence, film-substrate sensitivity, and reproducibility.

Main claims

  • Superconductivity in Ruddlesden-Popper nickelates appears only when the local constrained deformation of the Ni-O framework falls within a bounded shear-strain window.
    • Evidence: Experimental evidence from NV quantum sensing shows superconductivity disappears when shear stress exceeds ≈2 GPa and is also weakened when shear stress approaches zero
  • The shear-stress-constrained superconductivity (SSCS) scenario unifies the understanding of pressure threshold, reversibility, spatial inhomogeneity, pressure-medium dependence, film-substrate sensitivity, and reproducibility.
    • Evidence: Framework explains why ambient-pressure tetragonal phase does not superconduct under pressure; why films need less external pressure; why chemical substitution and hybrid structures enhance T_c

Workflow

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