Type-I superconductivity in noncentrosymmetric superconductor

The noncentrosymmetric superconductor AuBe have been investigated using the magnetization, resistivity, specific heat, and muon-spin relaxation/rotation measurements. AuBe crystallizes in the cubic FeSi-type B20 structure with superconducting transition temperature observed at Tc = 3.2 ± 0.1 K. The low-temperature specific heat data, Cel(T), indicate a weakly-coupled fully gapped BCS superconductivity with an isotropic energy gap 2∆(0)/kBTc = 3.76, which is close to the BCS value of 3.52. Interestingly, type-I superconductivity is inferred from the μSR measurements, which is in contrast with the earlier reports of type-II superconductivity in AuBe. The Ginzburg-Landau parameter is κGL = 0.4 < 1/ √ 2. The transverse-field μSR data transformed in the maximum entropy spectra depicting the internal magnetic field probability distribution, P(H), also confirms the absence of the mixed state in AuBe. The thermodynamic critical field, Hc, calculated to be around 259 Oe. The zero-field μSR results indicate that time-reversal symmetry is preserved and supports a spin-singlet pairing in the superconducting ground state.