Bridging ambient- and high-pressure superconductivity in La2LnNi2O7 films.

Abstract

The discovery of high-critical-temperature (high-Tc) superconductivity near 80 K in bilayer nickelates under high pressure has sparked extensive studies. Whereas superconductivity exceeding 40 K was subsequently discovered at ambient pressure in compressively strained films, the relationship between ambient- and high-pressure regimes remains an open question. Here we present a systematic investigation of superconductivity in compressively strained La2LnNi2O7 films (where Ln is a lanthanide) at ambient and high pressures. The normal-state resistivity at ambient pressure, revealed by suppressing the superconductivity with magnetic fields of 59 T, tends towards T2 behaviour. Under high pressure in a cubic anvil cell, Tc was enhanced from 41-42 K at ambient pressure to 67-73 K at 16 GPa. On the other hand, lattice compression induced by Ln substitution, which may mimic the effects of pressure, lowers Tc. In both cases, Tc correlates with the evolution of normal-state transport between T2 and T-linear behaviour, offering insight into the interplay between lattice structure and superconductivity in bilayer nickelates.