131 research outputs found

    Superconductivity in the Nb-Ru-Ge σ\sigma-Phase

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    We show that the previously unreported ternary σ\sigma-phase material Nb20.4_{20.4}Ru5.7_{5.7}Ge3.9_{3.9} is a superconductor with a critical temperature of 2.2 K. Temperature-dependent magnetic susceptibility, resistance, and specific heat measurements were used to characterize the superconducting transition. The Sommerfeld constant γ\gamma for Nb20.4_{20.4}Ru5.7_{5.7}Ge3.9_{3.9} is 91 mJ mol-f.u.1^{-1}K2^{-2} and the specific heat anomaly at the superconducting transition, Δ\DeltaC/γ\gammaTc_c, is approximately 1.38. The zero-temperature upper critical field (μ0\mu_0Hc2_{c2}(0)) was estimated to be 2 T by resistance data. Field-dependent magnetization data analysis estimated μ0\mu_0Hc1_{c1}(0) to be 5.5 mT. Thus, the characterization shows Nb20.4_{20.4}Ru5.7_{5.7}Ge3.9_{3.9} to be a type II BCS superconductor. This material appears to be the first reported ternary phase in the Nb-Ru-Ge system, and the fact that there are no previously reported binary Nb-Ru, Nb-Ge, or Ru-Ge σ\sigma-phases shows that all three elements are necessary to stabilize the material. A σ\sigma-phase in the Ta-Ru-Ge system was synthesized but did not display superconductivity above 1.7 K, which suggests that electron count cannot govern the superconductivity observed. Preliminary characterization of a possible superconducting σ\sigma-phase in the Nb-Ru-Ga system is also reported.Comment: 7 pages, 8 figures, 3 table

    Possible singlet to triplet pairing transition in NaxCoO2 H2O

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    We present precise measurements of the upper critical field (Hc2) in the recently discovered cobalt oxide superconductor. We have found that the critical field has an unusual temperature dependence; namely, there is an abrupt change of the slope of Hc2(T) in a weak field regime. In order to explain this result we have derived and solved Gor'kov equations on a triangular lattice. Our experimental results may be interpreted in terms of the field-induced transition from singlet to triplet superconductivity.Comment: 6 pages, 5 figures, revte

    Superconductivity in Mg10Ir19B16

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    Mg10Ir19B16, a previously unreported compound in the Mg-Ir-B chemical system, is found to be superconducting at temperatures near 5 K. The fact that the compound exhibits a range of superconducting temperatures between 4 and 5 K suggests that a range of stoichiometries is allowed, though no structural evidence for this is observed. The compound has a large, noncentrosymmetric, body centered cubic unit cell with a = 10.568 Angstrom, displaying a structure type for which no previous superconductors have been reported.Comment: submitted to PR

    A greater decline in female facial attractiveness during middle age reflects women’s loss of reproductive value

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    Facial attractiveness represents an important component of an individual’s overall attractiveness as a potential mating partner. Perceptions of facial attractiveness are expected to vary with age-related changes in health, reproductive value, and power. In this study, we investigated perceptions of facial attractiveness, power, and personality in two groups of women of pre- and post-menopausal ages (35–50 years and 51–65 years, respectively) and two corresponding groups of men. We tested three hypotheses: (1) that perceived facial attractiveness would be lower for older than for younger men and women; (2) that the age-related reduction in facial attractiveness would be greater for women than for men; and (3) that for men, there would be a larger increase in perceived power at older ages. Eighty facial stimuli were rated by 60 (30 male, 30 female) middle-aged women and men using online surveys. Our three main hypotheses were supported by the data. Consistent with sex differences in mating strategies, the greater age-related decline in female facial attractiveness was driven by male respondents, while the greater age-related increase in male perceived power was driven by female respondents. In addition, we found evidence that some personality ratings were correlated with perceived attractiveness and power ratings. The results of this study are consistent with evolutionary theory and with previous research showing that faces can provide important information about characteristics that men and women value in a potential mating partner such as their health, reproductive value, and power or possession of resources
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