Fig. 1: Phase transition from topological Dirac semimetal α-Sn to superconducting metal β-Sn induced by irradiation of a Ga-focused ion beam (FIB).
a Schematic image of α-Sn/β-Sn planar nanostructures fabricated by FIB irradiation. b, c Top-view scanning electron microscopy (SEM) images of (b) β-Sn/α-Sn/β-Sn Josephson junction structure with an α-Sn width of 70 nm and (c) a 180 nm-wide β-Sn nanowire embedded in α-Sn (see “Methods”). d X-ray photoemission spectroscopy (XPS) measurements of the valence band spectrum of α-Sn and β-Sn regions, compared with an Au reference film. The Fermi level EF (vertical red line) is determined from the Fermi-Dirac edge of the Au film. A large DOS is detected at EF of the irradiated Sn, reflecting the metallic behaviour of β-Sn. e Cross-sectional scanning transmission electron microscopy (STEM) lattice image of the interface region between α-Sn/β-Sn prepared by FIB irradiation. The as-grown α-Sn retains its diamond-type crystal structure (yellow-square inset), while the FIB-irradiated region changes to polycrystalline β-Sn (red-square inset). An abrupt interface between α-Sn/β-Sn region is obtained. f Temperature dependence of the resistance of the β-Sn wires with various wire widths. Inset shows the detailed data around the superconducting transition. All the wires undergo a superconducting transition below 4 K.
