Noncentrosymmetric superconductor BeAu

Mixed spin-singlet and spin-triplet pairing can occur in noncentrosymmetric superconductors. In this respect, a comprehensive characterization of the noncentrosymmetric superconductor BeAu was carried out. It was established that BeAu undergoes a structural phase transition from a low-temperature noncentrosymmetric FeSi structure type to a high-temperature centrosymmetric structure in the CsCl type at ${T}_{\text{s}}=860$ K. The low-temperature modification exhibits a superconducting transition below ${T}_{\text{c}}=3.3$ K. The values of lower (${H}_{\text{c1}}=32$ Oe) and upper (${H}_{\text{c2}}=335$ Oe) critical fields are rather small, confirming that this type-II (${\ensuremath{\kappa}}_{\text{G-L}}=2.3$) weakly coupled (${\ensuremath{\lambda}}_{\text{e-p}}=0.5,\phantom{\rule{0.28em}{0ex}}\mathrm{\ensuremath{\Delta}}{C}_{\text{e}}/{\ensuremath{\gamma}}_{\text{n}}{T}_{\text{c}}\ensuremath{\approx}1.26$) superconductor can be well understood within the Bardeen-Cooper-Schrieffer theory. The muon spin relaxation analysis indicates that the time-reversal symmetry is preserved when the superconducting state is entered, supporting conventional superconductivity in BeAu. From the density functional band structure calculations, a considerable contribution of the Be electrons to the superconducting state was established. On average, a rather small mass renormalization was found, consistent with the experimental data.