Superconductivity in WBe2

TL;DR

This study reports the discovery of bulk superconductivity in WBe2 at ambient pressure with a Tc around 0.86-1.05 K, achieved by careful sample preparation to avoid known superconducting phases.

Contribution

First demonstration of bulk superconductivity in WBe2 at ambient pressure, with detailed characterization confirming its properties and phase purity.

Findings

WBe2 is a bulk superconductor at ambient pressure.

Superconducting transition temperature (Tc) is approximately 0.86-1.05 K.

Upper critical field is about 400 gauss.

Abstract

WBe2, which occurs in space group 194, with hexagonal symmetry P63/mmc, is prepared by arc-melting at temperatures above 2200 C, where Be vapor loss is significant. This study is motivated by recent work on MoB2 and WB2, both superconductors (Tc=32 and 17 K respectively) under high (~70 GPa) pressure. In order to avoid the known Be-rich superconducting phases (WBe13 and WBe22) in the complex phase diagram, both known to be superconducting at 4.1 K, the sample was prepared with a slight (~5%) excess of W. The resultant sample, prepared using high purity (99.999%) Be, is essentially single phase WBe2, with some spread in its superconducting properties due to the known homogeneity range. (WBe2 forms in space group 194 between approximately W1.02Be1.98 and W0.88Be2.12.) Characterization was carried out with x-ray diffraction, electrical resistivity, rho, in zero and applied magnetic fields, and specific heat. The resistivity in zero and applied fields and specific heat data indicate that our sample of WBe2 is a bulk superconductor at ambient pressure with a Tc(onset) in the resistivity at 1.05 K, and Tc(rho->0) at ~0.86 K. There is no signature of superconductivity in rho at 4.1 K, indicating successful avoidance of WBe13 and WBe22. The resistivity data in field indicate an upper critical field of approximately 400 gauss.