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.

No 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]

No abstract

This is a copy of the published version, or version of record, available on the publisher's website. This version does not track changes, errata, or withdrawals on the publisher's site.

High entropy alloys (HEAs) are the new class of materials with an attractive combination of tunable mechanical and physicochemical properties. They crystallize mainly in cubic structures, however, for practical applications, HEAs with hexagonal close-packed (hcp) structure are highly desirable in connection to their in general high hardness. Herein, we report the synthesis, structure and detailed superconducting properties of Re0.56Nb0.11Ti0.11Zr0.11Hf0.11-the first hexagonal superconducting high entropy alloy (HEA) composed of five randomly distributed transition-metals. Combination of room temperature precession electron diffraction, precession electron diffraction tomography and powder X-ray diffraction is utilized to determine the room temperature crystal structure. Transport, magnetic and heat capacity measurements show that the material is a type-II superconductor with the bulk superconducting transition at Tc = 4.4 K, lower critical field Hc1(0) = 2.3 mT and upper critical field Hc2(0) = 3.6 T. Low-temperature specific heat measurement indicates that Re0.56Nb0.11Ti0.11Zr0.11Hf0.11 is a phonon-mediated superconductor in the weak electron-phonon coupling limit with a normalized specific heat jump ∆C el γnTc = 1.32. Further, hexagonal to cubic structural transition is observed by lowering the valence electron counts and Tc follows crystalline-like behaviour.

This work presents the emergence of superconductivity in Re substituted topological Weyl semimetal MoTe2. Re substitution for Mo sites lead to a sizable enhancement in the superconducting transition temperature (Tc). A record high Tc at ambient pressure in a 1T -MoTe2 (room temperature structure) related sample is observed for the Mo0.7Re0.3Te2 composition (Tc = 4.1 K, in comparison MoTe2, shows a Tc of 0.1 K). The experimental and theoretical studies indicate that Re substitution is doping electrons and facilitates the emergence of superconductivity by enhancing the electronphonon coupling and density of states at the Fermi level. Our findings, therefore, open a new way to further manipulate and enhance the superconducting state together with the topological states in 2D van der Waals materials.