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/γTc = 1.56, which is somewhat higher than what is expected for weakly coupled Bardeen–Cooper–Schrieffer type superconductors. The Hc2 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 (μ0Hc2(0)) for WB4.2 lies somewhere between the linear extrapolation of μ0Hc2(T) to 0 K and expectations based on the Werthamer–Helfand–Hohenberg model.