Surface and bulk superconductivity at ambient pressure in the Weyl semimetal TaP

Since the discovery of topological Weyl semimetal states in the compounds TaAs, TaP, NbAs and NbP, a considerable effort has been made to investigate their novel electronic properties. Of particular interest to this field is the search for a superconducting state, as such a state may host Majorana fermions. This search has led to observations of superconductivity in TaP under extreme pressure and after ion bombardment, but has hitherto failed to find a bulk superconductor at ambient pressure. We report on the observation of a superconducting state in Tantalum Phosphide (TaP) without any additional treatment to the material or under any extreme conditions. A Tc varying between 1.7 and 5.3 K for different samples was observed, both for microscopic samples processed with focused ion beam (FIB) etching as well as for an as-grown crystal. Our data show that the superconductivity present in our untreated crystal is inhomogeneous yet exists in the bulk. For samples made with FIB, we observe additionally a two-dimensional superconducting film on the sample surface.