Relationship between ambient- and high-pressure superconductivity in strained bilayer nickelate films

Determine whether the superconducting state of compressively strained mathrm{La_2LnNi_2O_7} thin films at ambient pressure is intrinsically consistent with the superconducting state observed in bulk bilayer nickelates under high pressure.

Background

High-temperature superconductivity was first observed in bilayer nickelates such as mathrm{La_3Ni_2O_7} under high pressure, whereas subsequent work established superconducting transitions above 40 K in compressively strained bilayer nickelate thin films at ambient pressure. These two experimental regimes involve different lattice responses: hydrostatic pressure compresses both the in-plane and out-of-plane lattice constants, while epitaxial strain primarily compresses the in-plane lattice and produces out-of-plane elongation through the Poisson effect.

The paper compares ambient-pressure superconductivity in epitaxially strained mathrm{La_2LnNi_2O_7} films with pressure-enhanced superconductivity in the same film systems. Although the authors observe related trends in normal-state transport and superconducting transition temperature, they explicitly leave unresolved whether the superconducting states in the two regimes are intrinsically the same.