Type-I superconductivity in the noncentrosymmetric superconductor BeAu

Abstract

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, C el (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. arXiv:1901.06492v1 [cond-mat.supr-con]

Single-gap versus two-gap scenario: Specific heat and thermodynamic critical field of the noncentrosymmetric superconductor BeAu

“…the value of α = 1.686( 8) is only slightly smaller than the weakly coupled BCS value α BCS = 1.764. This agrees with the previous observations suggesting the presence of a single isotropic energy gap in BeAu [46][47][48][49].…”

“…[47,50], respectively. Note that currently, three sets of C e (T ) and B c (T ) data for BeAu are available in the literature [46][47][48][49][50][51]. Among them, the C e (T ) and B c (T ) dependences from Refs.…”

“…Our interest in interpreting the superfluid density, the specific heat, and the thermodynamic critical field within the single-gap and two-gap scenarios was initiated by recent publications pointing to contradictory results for the noncentrosymmetric BeAu superconducting compound [46][47][48][49][50]. Indeed, Refs.…”

“…[46][47][48][49] consider BeAu to host a single isotropic gap, which is a characteristic of predominantly s-wave spinsinglet pairing in the weak-coupling limit. Such evidence comes from the electronic specific heat measurements, suggesting that C e (T ) is well described within the single-gap * rustem.khasanov@psi.ch approach with the ratio α = (0)/k B T c ranging from the weakly coupled BCS value α BCS = 1.764 up to α 1.88 [46][47][48][49]. Here, (0), T c , and k B are the zero-temperature value of the gap, the superconducting transition temperature, and the Boltzmann constant, respectively.…”

Coexistence of type-I and type-II superconductivity signatures in ZrB12 probed by muon spin rotation measurements

“…This technique has been widely used to map the phase diagram and study the microscopic properties of the vortex and Meissner state of superconductors [32,33]. Investigations of the intermediate state by μSR have been limited to a few elemental superconductors [34][35][36][37]; however, recently, there has been increased attention in conjunction with the nature of the superconductivity of the noncentrosymmetric BeAu [38,39]. Here, we employed μSR spectroscopy on single crystals of ZrB 12 , mapped the inhomogeneous magnetic field distributions, and identified and characterized the different superconducting states in the H-T phase diagram.…”