19 research outputs found

    Structure and superconductivity in the binary Re1x_{1-x}Mox_x alloys

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    The binary Re1x_{1-x}Mox_x alloys, known to cover the full range of solid solutions, were successfully synthesized and their crystal structures and physical properties investigated via powder x-ray diffraction, electrical resistivity, magnetic susceptibility, and heat capacity. By varying the Re/Mo ratio we explore the full Re1x_{1-x}Mox_x binary phase diagram, in all its four different solid phases: hcp-Mg (P63/mmcP6_3/mmc), α\alpha-Mn (I43mI\overline{4}3m), β\beta-CrFe (P42/mnmP4_2/mnm), and bcc-W (Im3mIm\overline{3}m), of which the second is non-centrosymmetric with the rest being centrosymmetric. All Re1x_{1-x}Mox_x alloys are superconductors, whose critical temperatures exhibit a peculiar phase diagram, characterized by three different superconducting regions. In most alloys the TcT_c is almost an order of magnitude higher than in pure Re and Mo. Low-temperature electronic specific-heat data evidence a fully-gapped superconducting state, whose enhanced gap magnitude and specific-heat discontinuity suggest a moderately strong electron-phonon coupling across the series. Considering that several α\alpha-Mn-type ReTT alloys (TT = transition metal) show time-reversal symmetry breaking (TRSB) in the superconducting state, while TRS is preserved in the isostructural Mg10_{10}Ir19_{19}B16_{16} or Nb0.5_{0.5}Os0.5_{0.5}, the Re1x_{1-x}Mox_x alloys represent another suitable system for studying the interplay of space-inversion, gauge, and time-reversal symmetries in future experiments expected to probe TRSB in the ReTT family.Comment: 8 pages, 7 figures, accepted for publication on Physical Review Material

    Nodeless superconductivity and preserved time-reversal symmetry in the noncentrosymmetric Mo3P superconductor

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    We report a comprehensive study of the noncentrosymmetric superconductor Mo3_3P. Its bulk superconductivity, with Tc=5.5T_c = 5.5 K, was characterized via electrical resistivity, magnetization, and heat-capacity measurements, while its microscopic electronic properties were investigated by means of muon-spin rotation/relaxation (μ\muSR) and nuclear magnetic resonance (NMR) techniques. In the normal state, NMR relaxation data indicate an almost ideal metallic behavior, confirmed by band-structure calculations, which suggest a relatively high electron density of states, dominated by the Mo 4d4d-orbitals. The low-temperature superfluid density, determined via transverse-field μ\muSR and electronic specific heat, suggest a fully-gapped superconducting state in Mo3_3P, with Δ0=0.83\Delta_0= 0.83 meV, the same as the BCS gap value in the weak-coupling case, and a zero-temperature magnetic penetration depth λ0=126\lambda_0 = 126 nm. The absence of spontaneous magnetic fields below the onset of superconductivity, as determined from zero-field μ\muSR measurements, indicates a preserved time-reversal symmetry in the superconducting state of Mo3_3P and, hence, spin-singlet pairing.Comment: 13 pages, 16 figures, accepted by Phys. Rev.

    Enhanced skyrmion metastability under applied strain in FeGe

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    Mechanical straining of skyrmion hosting materials has previously demonstrated increased phase stability through the expansion of the skyrmion equilibrium pocket. Additionally, metastable skyrmions can be generated via rapid field cooling to form significant skyrmion populations at low temperatures. Using small-angle x-ray scattering and x-ray holographic imaging on a thermally strained 200-nm-thick FeGe lamella, we observe temperature-induced strain effects on the structure and metastability of the skyrmion lattice. We find that in this sample orientation ( H ∥ [ ¯ 1 1 0 ] ) with no strain, metastable skyrmions produced by field cooling through the equilibrium skyrmion pocket vanish from the sample upon dropping below the well-known helical reorientation temperature. However, when strain is applied along the [ 1 1 0 ] axis, and this procedure is repeated, a substantial volume fraction of metastable skyrmions persist upon cooling below this temperature down to 100 K. Additionally, we observe a large number of skyrmions retained after a complete magnetic field polarity reversal, implying that the metastable energy barrier protecting skyrmions from decay is enhanced

    Broken time-reversal symmetry in cubic skutterudite-like superconductor Y3_3Ru4_4Ge13_{13}

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    The microscopic properties of superconducting cubic skutterudite-like material Y3_3Ru4_4Ge13_{13} are investigated using muon spin relaxation and rotation (μ\muSR) measurements. Zero-field μ\muSR measurements reveal the presence of a spontaneous internal field with a magnitude of \approx 0.18~mT below the superconducting transition temperature, indicating broken time-reversal symmetry in the ground state. In line with previous experiments, transverse-field μ\muSR measurements are consistent with a fully developed superconductivity gap in Y3_3Ru4_4Ge13_{13}. Our observations point towards the relevance of electronic correlations beyond electron-phonon coupling as origin and indicate that spin-orbit coupling is likely not the key driving force behind the spontaneous breaking of time-reversal symmetry in this system.Comment: 7 pages, 3 figure

    Time-reversal symmetry breaking in superconducting low-carrier-density quasi-skutterudite Lu3Os4Ge13

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    The complex structure of the Remeika phases, the intriguing quantum states they display, and their low carrier concentrations are a strong motivation to study the nature of their superconducting phases. In this work, the microscopic properties of the superconducting phase of single-crystalline Lu3_3Os4_4Ge13_{13} are investigated by muon-spin relaxation and rotation (μ\muSR) measurements. The zero-field μ\muSR data reveal the presence of spontaneous static or quasi-static magnetic fields in the superconducting state, breaking time-reversal symmetry; the associated internal magnetic field scale is found to be exceptionally large (\approx 0.18~mT). Furthermore, transverse-field μ\muSR measurements in the vortex state of Lu3_3Os4_4Ge13_{13} imply a complex gap function with significantly different strengths on different parts of the Fermi surface. While our measurements do not completely determine the order parameter, they strongly indicate that electron-electron interactions are essential to stabilizing pairing in the system, thus, demonstrating its unconventional nature.Comment: 7 pages, 2 figure
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