Superconductivity in WP single crystals

Abstract

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 ${T}_{\text{c}}\ensuremath{\sim}0.8\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ 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 ${\ensuremath{\mu}}_{0}{H}_{\text{c}2,\ensuremath{\parallel}}=17.2\phantom{\rule{0.28em}{0ex}}\mathrm{mT}$ and ${\ensuremath{\mu}}_{0}{H}_{\text{c}2,\ensuremath{\perp}}=8.5\phantom{\rule{0.28em}{0ex}}\mathrm{mT}$, 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.