Unconventional superconductivity in La3Ni2O7 from the perspective of symmetry

Abstract

The recently discovered superconductor La3Ni2O7 has attracted significant attention due to its remarkably high transition temperature (Tc) under high pressure. Shortly after this discovery, thin-film La3Ni2O7 was demonstrated to exhibit ambient-pressure superconductivity; however, the corresponding Tc is only about half that of the pressurized bulk material. This striking difference raises questions about the underlying mechanisms governing superconductivity in these two structures. To address this issue, we develop a phenomenological symmetry-based method to investigate the superconducting gap structure in La3Ni2O7. Using density-functional theory methods (DFT+U), together with the experimentally determined Tc and structural symmetry, we find that both pressurized bulk and thin-film La3Ni2O7 exhibit s±-wave pairing symmetry and two-gap superconductivity, yet their dominant microscopic pairing configurations are distinct. In the pressurized bulk, superconductivity is dominated by the out-of-plane pairing of the Ni-dz2 orbitals, while in the thin film, the in-plane pairing of the Ni-dx2−y2 orbitals prevails. Furthermore, the observed reduction in Tc can be attributed to this transition of the dominant pairing type, driven by the decreased ratio of interlayer to intralayer hoppings in the thin film. Our result sheds lights on the microscopic pairing in La3Ni2O7 and reveals the significance of the symmetry. This method can potentially be generalized to a broader range of unconventional superconductors.

Source-reported materials — not catalogue approval

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