Two-gap superconductivity and topological surface states in TaOsSi

The occurrence of superconductivity in topological materials is considered as a promising route for realizing topological superconductors, a platform able to host the long-sought Majorana fermions in condensed matter. In this work, by using electrical transport and heat-capacity measurements, as well as first-principles band-structure calculations, we investigate the physical properties of TaOsSi, a superconductor with Tc≈5.8 K. The behavior of both its upper critical field and low-temperature heat-capacity suggest the existence of two superconducting gaps. More strikingly, first-principles calculations reveal gapless topological surface states in the present material. The evolution of the electrical resistivity with pressure (up to 50 GPa) was also investigated, and a ``V-shaped'' diagram of Tc vs P was found. Overall, our data suggest that TaOsSi is a new system where multiband superconductivity and topological surface states coexist and, hence, it may serve as a possible candidate in the search for topological superconductivity.