Scanning tunnelling spectroscopy of superconductivity on surfaces of LiTi2O4(111) thin films

Unique superconductivity at surfaces/interfaces, as exemplified by LaAlO 3 /SrTiO 3 interfaces, and the high transition temperature in ultrathin FeSe films, have triggered intense debates on how superconductivity is affected in atomic and electronic reconstructions. The surface of superconducting cubic spinel oxide LiTi 2 O 4 is another interesting system because its inherent surface electronic and atomic reconstructions add complexity to superconducting properties. Investigations of such surfaces are hampered by the lack of single crystals or high-quality thin films. Here, using low-temperature scanning tunnelling microscopy and spectroscopy, we report an unexpected small superconducting energy gap and a long coherence length on the surface of LiTi 2 O 4 (111) epitaxial thin films. Furthermore, we find that a pseudogap opening at the Fermi energy modifies the surface superconductivity. Our results open an avenue for exploring anomalous superconductivity on the surface of cubic transition-metal oxides, where the electronic states are spontaneously modulated involving rich many-body interactions. Atomic and electronic reconstructions at surfaces/interfaces bring about various emergent phenomena. Here, Okada et al . report an unexpected superconducting gap and a long coherence length on the surface of LiTi 2 O 4 (111) thin films.