Superconducting transition in a topological Dirac semimetal α-Sn thin film*

Topological superconductivity (TSC) gathers much attention due to its potential application to topological quantum computing. One of the candidates for TSC is doped topological Dirac semimetal (TDS) [1]. In this study, we have discovered superconductivity in an elemental TDS α-Sn thin film (~ 5 nm) grown on an InSb (001) substrate. The as-grown α-Sn thin film showed semiconducting behavior, but it showed superconductivity (T_C = 4.2 K) 20 months later, probably caused by In diffusion into the α-Sn layer while the diamond crystal structure is maintained. Temperature dependence of the critical magnetic field is well explained by the 2D superconductivity model with GL coherence length of 20.5 nm. The in-plane critical magnetic field at 0 K estimated by the fitting reaches 11.8 T, which is far beyond the Pauli-limiting field H_P = 1.86T_C ~ 7.8 T. This indicates that paramagnetic pair-breaking effect is suppressed by the spin-orbit interaction of α-Sn. We observed Shubnikov-de Haas oscillations, indicating that the Fermi level has shifted by the aging, and a new linear band has appeared which may be the origin of superconductivity, considering calculated coherence length. Our result suggests that α-Sn is promising for TSC and quantum computing material.

[1] T. Hashimoto, et al., Phys. Rev. B 94, 014510 (2016).