Superconducting fluctuation corrections to ultrasound attenuation in layered superconductors

We consider the temperature dependence of the sound attenuation and sound velocity in layered impure metals due to superconducting fluctuations of the order parameter above the critical temperature. We obtain the dependence on material properties of these fluctuation corrections in the hydrodynamic limit, where the electron mean free path is much smaller than the wavelength of sound and where the electron collision rate is much larger than the sound frequency. For longitudinal sound propagating perpendicular to the layers, the open Fermi surface condition leads to a suppression of the divergent contributions to leading order, in contrast with the case of paraconductivity. The leading temperature dependent corrections, given by the Aslamazov-Larkin, Maki-Thompson and density of states terms, remain finite as T->Tc. Nevertheless, the sensitivity of new ultrasonic experiments on layered organic conductors should make these fluctuations effects measurable.Comment: 13 pages, 6 figures. Accepted for PRB. Added discussion on incoherent interlayer tunneling and other small modifications suggested by referee

Antiferromagnetic Domains and Superconductivity in UPt3

We explore the response of an unconventional superconductor to spatially inhomogeneous antiferromagnetism (SIAFM). Symmetry allows the superconducting order parameter in the E-representation models for UPt3 to couple directly to the AFM order parameter. The Ginzburg-Landau equations for coupled superconductivity and SIAFM are solved numerically for two possible SIAFM configurations: (I) abutting antiferromagnetic domains of uniform size, and (II) quenched random disorder of `nanodomains' in a uniform AFM background. We discuss the contributions to the free energy, specific heat, and order parameter for these models. Neither model provides a satisfactory account of experiment, but results from the two models differ significantly. Our results demonstrate that the response of an E_{2u} superconductor to SIAFM is strongly dependent on the spatial dependence of AFM order; no conclusion can be drawn regarding the compatibility of E_{2u} superconductivity with UPt3 that is independent of assumptions on the spatial dependence of AFMComment: 12 pages, 13 figures, to appear in Phys. Rev.

Meeting deadlines in work groups: Implicit and explicit mechanisms

Nous nous sommes demandés, dans cette étude, si les groupes étaient mieux à même de respecter les délais quand leurs membres partageaient les mêmes cognitions temporelles, c’est-à-dire quand ils s’accordaient sur les dimensions temporelles de leur tâche. Dans une étude longitudinale portant sur 31 groupes, nous avons étudié l’effet des cognitions temporelles partagées sur le respect d’un délai et exploré deux antécédents des cognitions temporelles partagées: la cohérence des rythmes des membres du groupe et l’échange des rappels concernant le temps. Nos résultats montrent que ces deux facteurs ont un impact sur les cognitions temporelles partagées et cela à différentes étapes du travail collectif. De plus, il est apparu que les cognitions temporelles partagées pouvaient aussi bien faciliter que contrecarrer le respect des délais: cela dépend des rythmes des membres du groupe. In this study, we examined whether groups were better able to meet deadlines when group members had shared temporal cognitions, that is, when they agreed on the temporal aspects of their task. In a longitudinal study involving 31 groups, we studied the effect of shared temporal cognitions on meeting a deadline and explored two antecedents of shared temporal cognitions: the similarity in group members’ pacing styles and the exchange of temporal reminders. Our findings suggest that both antecedents are relevant to shared temporal cognitions, be it at different stages of group collaboration. Furthermore, we found that shared temporal cognitions may either facilitate or impede meeting a deadline, depending on the content of group members’ pacing styles