Jupiter's Obliquity and a Long-lived Circumplanetary Disk

It has been claimed (Canup and Ward 2002; Ward 2003) that a long-lived massive (compared to the mass of the Galilean satellites) circumplanetary gas disk is inconsistent with Jupiter's low obliquity. Such a constraint could be downplayed on the basis that it deals with a single observation. Here we argue that this argument is flawed because it assumes a solar system much like that of the present day with the one exception of a circumjovian disk which is then allowed to dissipate on a long timescale (10^6-10^7 yrs). Given that the sequence of events in solar-system history that fit known constraints is non-unique, we choose for the sake of clarity of exposition the orbital architecture framework of Tsiganis et al. (2005), in which Jupiter and Saturn were once in closer, less inclined orbits than they are at present, and show that Jupiter's low obliquity is consistent with the SEMM (solids-enhanced minimum mass) satellite formation model of Mosqueira and Estrada (2003a,b).Comment: 8 pages, 1 figure. Submitted note to Icaru

Magnetization vector in the reversible region of a highly anisotropic cuprate superconductor: anisotropy factor and the role of 2D vortex fluctuations

By using a high quality Tl2Ba2Ca2Cu3O10 (Tl-2223) single crystal as an example, the magnetization vector was probed in the reversible region of highly anisotropic cuprate superconductors. For that, we have measured its components along and transverse to the applied magnetic field for different crystal orientations. The analysis shows that the angular dependence of the perpendicular component of the magnetization vector follows the one predicted by a London-like approach which includes a contribution associated with the thermal fluctuations of the 2D vortex positions. For the Tl-2223 crystal studied here, a lower bound for the anisotropy factor was estimated to be about 190.Comment: 6 pages, 3 figure

On the dilemma between percolation processes and fluctuating pairs as the origin of the enhanced conductivity above the superconducting transition in cuprates

The confrontation between percolation processes and superconducting fluctuations to account for the observed enhanced in-plane electrical conductivity above but near $T_c$ in cuprates is revisited. The cuprates studied here, La$_{1.85}$Sr$_{0.15}$CuO$_4$, Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, and Tl$_2$Ba$_2$Ca$_2$Cu$_3$O$_{10}$, have a different number of superconducting CuO$_2$ layers per unit-cell length and different Josephson coupling between them, and are optimally-doped to minimize $T_c$-inhomogeneities. The excellent chemical and structural quality of these samples also contribute to minimize the effect of extrinsic $T_c$-inhomogeneities, a crucial aspect when analyzing the possible presence of intrinsic percolative processes. Our analyses also cover the so-called high reduced-temperature region, up to the resistivity rounding onset $\varepsilon_{onset}$. By using the simplest form of the effective-medium theory, we show that possible emergent percolation processes alone cannot account for the measured enhanced conductivity. In contrast, these measurements can be quantitatively explained using the Gaussian-Ginzburg-Landau (GGL) approach for the effect of superconducting fluctuations in layered superconductors, extended to $\varepsilon_{onset}$ by including a total energy cutoff, which takes into account the limits imposed by the Heisenberg uncertainty principle to the shrinkage of the superconducting wavefunction. Our analysis confirms the adequacy of this cutoff, and that the effective periodicity length is controlled by the relative Josephson coupling between superconducting layers. These conclusions are reinforced by analyzing one of the recent works that allegedly discards the superconducting fluctuations scenario while supporting a percolative scenario for the enhanced conductivity above $T_c$ in cuprates.Comment: 13 pages, 7 figure

Comment on "High Field Studies of Superconducting Fluctuations in High-Tc Cuprates. Evidence for a Small Gap distinct from the Large Pseudogap"

By using high magnetic field data to estimate the background conductivity, Rullier-Albenque and coworkers have recently published [Phys.Rev.B 84, 014522 (2011)] experimental evidence that the in-plane paraconductivity in cuprates is almost independent of doping. In this Comment we also show that, in contrast with their claims, these useful data may be explained at a quantitative level in terms of the Gaussian-Ginzburg-Landau approach for layered superconductors, extended by Carballeira and coworkers to high reduced-temperatures by introducing a total-energy cutoff [Phys.Rev.B 63, 144515 (2001)]. When combined, these two conclusions further suggest that the paraconductivity in cuprates is conventional, i.e., associated with fluctuating superconducting pairs above the mean-field critical temperature.Comment: 9 pages, 1 figur

Enhancement of the critical current by surface irregularities in Fe-based superconductors

The critical current $I_c$ of single crystals of the iron pnictide superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$, has been studied through measurements of magnetic hysteresis cycles. We show that the introduction of surface irregularities in the $\mu$m scale significantly increase $I_c$, primarily near the irreversibility magnetic field $H_{irr}$, where the surface currents are the main contribution to $I_c$. Such an increase is consistent with a theoretical estimate for the maximum non-dissipative current that a rough surface can sustain, based on Mathieu-Simon continuum theory for the vortex state.Comment: 24 pages including 5 pages of supplementary materia