Strain-tuning for superconductivity in La3Ni2O7 thin films

The recent discovery of high-transition temperature (Tc) superconductivity in pressurized La3Ni2O7 bulk crystals has attracted keen attention for its characteristic energy diagram of eg orbitals containing nearly half-filled $${d}_{{3}{z}^{2}-{r}^{2}}$$ and quarter-filled $${d}_{{x}^{2}-{y}^{2}}$$ orbitals. This finding provides valuable insights into the orbital contributions and interlayer interactions in double NiO6 octahedrons that further provides a chance to control the electronic structure via varying ligand field. Here, we demonstrate that strain-tuning of the Tc over a range of 50 K with La3Ni2O7 films on different oxide substrates under 20 GPa. As the c/a ratio increases, the onset Tc systematically increases from 10 K in the tensile-strained film on SrTiO3 to the highest value about 60 K in the compressively strained film on LaAlO3. These systematic variations suggest that strain-engineering is a promising approach for expanding the superconductivity in bilayer nickelates with tuning the energy diagram for achieving high-Tc superconductivity. The discovery of superconductivity in the nickelates not only offers a new family of materials to explore but the opportunity to gain further insight into the mechanisms of unconventional superconductivity. Here, the authors employ epitaxial strain to investigate superconductivity in La3Ni2O7 thin films and discuss how changes to the lattice parameters of the parent structure can impact on the observed properties.