Superconductivity in the superhard boride WB4.2

Abstract

We show that the superhard boride WB4.2 is a superconductor with a Tc of 2.05(5) K. Temperature-dependent magnetic susceptibility, electrical resistivity, and specific heat measurements were used to characterize the superconducting transition. The Sommerfeld constant γ for WB4.2 is 2.07(3) mJ mol-1 K-2 and the ΔC/γ Tc = 1.56, which is somewhat higher than what is expected for weakly coupled Bardeen-Cooper-Schrieffer type superconductors. The H c2 versus T plot is linear over a wide temperature range but does show signs of flattening by the lowest temperatures studied and therefore the zero temperature upper critical field (μ 0 H c2(0)) for WB4.2 lies somewhere between the linear extrapolation of μ 0 H c2(T) to 0 K and expectations based on the Werthamer-Helfand-Hohenberg model.