Allotropic transition of Dirac semimetal -Sn to superconductor -Sn induced by focused-ion-beam irradiation

Diamond-type structure allotrope alpha-Sn is attracting much attention as a topological Dirac semimetal (TDS). In this study, we demonstrate that alpha-Sn undergoes a phase transition to another allotrope beta-Sn with superconductivity at low temperature by irradiating with a focused Ga ion beam (FIB). To clarify the transition mechanism, we performed x-ray photoemission spectroscopy (XPS) measurements on an alpha-Sn thin film irradiated with FIB and an as-grown alpha-Sn thin film. The XPS results suggest that the local annealing, which is one of the side effects of FIB, causes the transformation from alpha-Sn into beta-Sn. Furthermore, the difference in the chemical states between alpha-Sn and beta-Sn can be quantitatively explained by the crystal structures rather than the degree of metallicity reflecting the conductivity. These results propose a way of fabricating TDS/superconductor in-plane heterostructures based on alpha-Sn and beta-Sn.