Orientation-dependent superconductivity and electronic structure of the rare-earth metal/KTaO₃ interfaces

The recent discovery of orientation-dependent superconductivity in KTaO₃-based interfaces has attracted considerable interest, while the underlying origin remains an open question. Here we report a different approach to tune the interfacial electron gas and superconductivity by forming interfaces between rare-earth (RE) metals (RE being La, Ce, Eu) and KTaO₃substrates with different orientations. We found that the interfacial superconductivity is strongest for the Eu/KTaO₃interfaces, becomes weaker in La/KTaO₃and is absent in Ce/KTaO₃. Using<i>in-situ</i>photoemission, we observed distinct valence bands associated with RE metals, as well as a pronounced orientation dependence in the interfacial electronic structure, which can be linked to the orientation-dependent superconductivity. The photoemission spectra show similar double-peak structures for the (111) and (110) oriented interfaces, with an energy separation close to the LO4 phonon of KTaO₃. Detailed analyses suggest that this double-peak structure could be attributed to electron-phonon coupling, which might be relevant for the interfacial superconductivity.