Observing superconductivity in topological semimetal CoSi thin films

CoSi has recently emerged as a chiral topological semimetal (TSMs) demonstrating exotic quantum phenomena. Its unique crystal symmetry, being both chiral and non-centrosymmetric, gives rise to unique topological quasiparticle states. In this work, we present our study on textured CoSi ultra-thin films. By precise control of the growth temperature, we are able to selectively produce either CoSi (a TSM) or its centrosymmetric sibling, CoSi₂ (a trivial conductor). In electrical transport studies, we have observed multi-carrier transport in CoSi with one of the charge carriers demonstrating orders-of-magnitude higher mobility and thickness independent properties. In contrast, CoSi₂ only holds a low-mobility single-type charge carrier. The CoSi sample also shows unconventional magnetoresistance, which cannot be explained by classical transport models. Furthermore, we observe clear evidence of superconductivity in CoSi films. Through a set of comparative studies, we have confirmed that the superconductivity is intrinsic to CoSi. We will also show unconventional superconducting behaviors in CoSi, which distinguish it from other conventional superconductors. Our study reveals a new superconducting topological semimetal material.