Explain the compositional dependence of superconductivity in intergrowth phases

Explain why higher-order intergrowth phases in reduced trilayer nickelate crystals exhibit superconducting properties correlated with the bulk metal–insulator phase boundary of the 4-3-8 matrix in which they reside.

Background

Scanning transmission electron microscopy reveals square-planar intergrowth regions with thicknesses comparable to the superconducting layer thickness inferred from upper-critical-field measurements. Because strained infinite-layer-like intergrowths are known to support superconductivity, these defects are proposed as a possible source of the observed low-volume-fraction superconducting phase in (La1−xPrx)4Ni3O8 and (La1−xYx)4Ni3O8.

The unresolved issue is that superconductivity appears only near the bulk 4-3-8 metal–insulator phase boundary, whereas the intergrowths are higher-order phases. The paper does not establish why the superconducting properties of those intergrowths should vary compositionally in correlation with the phase behavior of the surrounding trilayer matrix.

References

An open question with the IG explanation is the compositional dependence of the superconductivity. Specifically, it is unclear why IGs of higher order phases should have compositional-based properties that are correlated to the underlying bulk metal-insulator phase boundary of the 4-3-8 matrix in which they reside.

— Superconductivity at the metal-insulator phase boundary in a bulk nickelate at ambient pressure  (2609.19686 - Ahn et al., 17 Sep 2026) in Discussion, subsection “Superconducting square-planar intergrowths”