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

TL;DR

This study uses low-temperature scanning tunneling microscopy to reveal unusual superconducting properties, including a small energy gap and pseudogap effects, on the surface of LiTi2O4(111) thin films, highlighting complex surface phenomena.

Contribution

First direct STM investigation of surface superconductivity on LiTi2O4(111) thin films revealing novel electronic features and pseudogap effects.

Findings

Small superconducting energy gap observed

Long coherence length detected

Pseudogap opening modifies surface superconductivity

Abstract

Unique superconductivity at surfaces/interfaces, as exemplified by LaAlO3/SrTiO3 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 LiTi2O4 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 tunneling microscopy, we report an unexpected small superconducting energy gap and a long coherence length on the surface of LiTi2O4 (111) epitaxial thin films. Furthermore, we find that a pseudogap opening at the Fermi energy modifies the surface superconductivity. Our results open an avenue, exploring anomalous superconductivity on the surface of cubic transition-metal oxides where the electronic states are spontaneously modulated with involving rich many-body interactions.