Self-forming superconducting microstructures from Weyl semimetals

Topological semi-metals host protected electronic states on their surface where the topology of the bulk bands is broken. By coupling them to a superconducting gap, exotic electronic excitations such as zero-energy Majorana modes can appear on the surface. In non-superconducting topological materials a gap can be induced via the proximity effect. A traditional path towards proximity-induced superconductivity involves growing a superconducting film on the non-superconducting topological material. We present a new way of fabricating superconducting microstructures from the non-superconducting Weyl-semimetal NbAs under Ga ion irradiation from a focused ion beam (FIB). Thereby As is preferentially removed from the surface, while the Nb-rich layer left behind shows robust type-II superconductivity with $T_c \sim$ 3K and $H_{c2} \sim$ 7T. In this approach the superconducting film self-forms on a single crystal, which may strongly influence the interface and coupling properties. Using this approach, we present a route towards fabricating superconducting topological nanowires.