Superconductivity in WP single crystals

We report the discovery of superconductivity in high-quality single crystals of transition-metal pnictides WP grown by chemical vapor transport method. Bulk superconductivity is observed at Tc∼0.8K at ambient pressure by electrical resistivity, ac magnetic susceptibility, and specific-heat measurements. The effects of magnetic field on the superconducting transitions are studied, leading to a large anisotropy parameter around 2 with the in-plane and out-of-plane upper critical fields of μ0Hc2, =17.2mT and μ0Hc2, =8.5mT, respectively. The low value of electron-phonon coupling estimated from the normal-state resistivity and specific-heat measurements suggest that WP is a weak-coupling BCS superconductor. Our finding demonstrates that WP is the first superconductor among 5d-transition metal pnictides with MnP-type structure at ambient pressure, which will help in the search for new superconductors in transition-metal pnictides.