Identify the microscopic ingredients of superconductivity in La3Ni2O7

Determine the essential microscopic ingredients responsible for superconductivity in the bilayer nickelate La3Ni2O7, specifying which structural and orbital factors govern the emergence of the superconducting state.

Background

La3Ni2O7 exhibits superconductivity under high pressure and, more recently, in strained thin films at ambient pressure, implicating structural and orbital degrees of freedom beyond those of single-layer systems. The material features strong interlayer hybridization of Ni d_{z^2} orbitals and Jahn–Teller splitting between e_g orbitals, both proposed as key to its electronic structure.

Despite intensive study, there is no consensus on which microscopic factors—such as interlayer d_{z^2} coupling, Jahn–Teller splitting, lattice strain, or their interplay—are primarily responsible for stabilizing superconductivity in La3Ni2O7. The paper frames this as an explicit open problem and investigates strain-tuned changes pointing to Jahn–Teller distortion as a key tuning parameter.