From ambient to high pressure: superconductivity in bilayer nickelate thin films

The recent discovery of high-transition temperature T_c superconductivity near 80 K in pressurized La₃Ni₂O₇ bulk crystals [1] has attracted keen attention due to its characteristic energy diagram involving d_3z²–r² and d_x²–y² orbitals [2]. Subsequently, superconductivity near 40 K was reported at ambient pressure in compressively strained films [3,4]. These findings provide valuable insights into the orbital contributions and interlayer interactions in double NiO₆ octahedra. Whereas hydrostatic pressure drives nearly isotropic lattice compression, epitaxial strain imposes biaxial in-plane constraints with out-of-plane elongation. In epitaxial thin films, the lattice strain can be finely tuned through substrate selection, enabling a controlled exploration of structural and electronic degrees of freedom that are challenging to access in bulk crystals. Combining this epitaxial strain control with external hydrostatic pressure offers a unique platform to disentangle anisotropic and isotropic lattice effects on superconductivity. In particular, investigating how isotropic compression influences films that already exhibit superconductivity under strong epitaxial strain provides crucial insight into the underlying mechanisms of high-T_c superconductivity. Within this context, we demonstrate a comprehensive strain-high-pressure approach in La₂LnNi₂O₇ thin films (Ln = lanthanides) grown on various oxide substrates, and apply pressures up to 20 GPa using a cubic-anvil cell [5]. Details of Ln dependence and transport measurements under ambient- and high-pressure conditions will be discussed in this presentation.