Concomitant appearance of conductivity and superconductivity in (111) LaAlO₃/SrTiO₃ interface with metal capping

In (111) SrTiO₃/LaAlO₃ interface, a critical thickness of nine monolayers (ML) of epitaxial LaAlO₃ is required for conductivity to appear. We show that this critical thickness always decreases when depositing a metallic over-layer. The critical thickness is only 3ML for cobalt overlayer and 6ML for platinum. The latter result contrasts with the (100) interface where a platinum overlayer increases the critical thickness beyond that of the bare interface [1]. These results suggest that the work function of the metallic overlayer plays an important role in both interfaces. Interestingly, for (111) SrTiO₃/LaAlO₃/Metal interfaces conductivity appears concomitantly with superconductivity in contrast with the (100) SrTiO₃/LaAlO₃/Metal interface with LaAlO₃ layer smaller than four unit-cells, which are conducting but not superconducting. We suggest that this difference is related to the different sub-bands involved in conductivity for the (111) interfaces comparing to the (100) interfaces [2]. Our findings can be useful for superconducting tunnelling devices.

References
1. D. C. Vaz et al., Adv. Mater., 29,1700486 (2017)
2. Udit Khanna et al., Phys. Rev. Lett., 123, 036805 (2019)