Copies of full items can be used for personal research or study, educational, or not-for-profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. The superconductivity of the noncentrosymmetric compound La7Ir3 has been investigated using muon spin rotation and relaxation (µSR). Zero-field measurements reveal the presence of spontaneous static or quasi-static magnetic fields below the superconducting transition temperature Tc = 2.25 K -a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic, and that the pairing symmetry of the superconducting electrons is predominantly s-wave with an enhanced binding strength. The results indicate that the superconductivity in La7Ir3 may be unconventional, and paves the way for further studies of this family of materials. Publisher

The discovery of new families of unconventional superconductors is important both experimentally and theoretically, especially if it challenges current models and thinking. By using muon spin relaxation in zero-field, time-reversal symmetry breaking has been observed in Re6Hf. Moreover, the temperature dependence of the superfluid density exhibits s-wave superconductivity with an enhanced electron-phonon coupling. This, coupled with the results from isostructural Re6Zr, shows that the Re6X family are indeed a new and important group of unconventional superconductors.

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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]