Z2 nontrivial topology of rare-earth binary oxide superconductor LaO

Recently, superconductivity has been discovered in rock-salt structured\nbinary lanthanum monoxide LaO through state-of-the-art oxide thin-film epitaxy.\nIn this work, we reveal that the normal state of superconducting LaO is a $Z_2$\nnontrivial topological metal, where the Dirac point protected by the crystal\nsymmetry is located around the Fermi energy. By analysing the orbital\ncharacteristics, we show that the nature of the topological band structure of\nLaO originates from the intra-atomic transition from the outer shell La 5$d$ to\nthe inner shell 4$f$ orbitals driven by the strong octahedral crystal-field.\nFurthermore, the appearance of novel surface states unambiguously demonstrates\nthe topological signature of LaO superconductor. Our theoretical findings not\nonly shed new light into the understanding of the exotic quantum behaviors in\nLaO superconductor with intimate correlation between 4$f$ and 5$d$ orbitals in\nLa, but also provide an exciting platform to explore the interplay between\nnontrivial topology and superconductivity.\n