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

On the energy saved by interlayer interactions in the superconducting state of cuprates

A Ginzburg-Landau-like functional is proposed reproducing the main low-energy features of various possible high-Tc superconducting mechanisms involving energy savings due to interlayer interactions. The functional may be used to relate these savings to experimental quantities. Two examples are given, involving the mean-field specific heat jump at Tc and the superconducting fluctuations above Tc. Comparison with existing data suggests, e.g., that the increase of Tc due to the so-called interlayer tunneling (ILT) mechanism of interlayer kinetic-energy savings is negligible in optimally-doped Bi-2212.Comment: 12 pages, no figures. Version history: 21-aug-2003, first version (available on http://arxiv.org/abs/cond-mat/0308423v1); 15-jan-2004, update to match Europhys. Lett. publication (minor grammar changes, updates in bibliography - e.g., refs. 5 and 26

Biaxial Strain in the Hexagonal Plane of MnAs Thin Films: The Key to Stabilize Ferromagnetism to Higher Temperature

The alpha-beta magneto-structural phase transition in MnAs/GaAs(111) epilayers is investigated by elastic neutron scattering. The in-plane parameter of MnAs remains almost constant with temperature from 100 K to 420 K, following the thermal evolution of the GaAs substrate. This induces a temperature dependent biaxial strain that is responsible for an alpha-beta phase coexistence and, more important, for the stabilization of the ferromagnetic alpha-phase at higher temperature than in bulk. We explain the premature appearance of the beta-phase at 275 K and the persistence of the ferromagnetic alpha-phase up to 350 K with thermodynamical arguments based on the MnAs phase diagram. It results that the biaxial strain in the hexagonal plane is the key parameter to extend the ferromagnetic phase well over room temperature.Comment: 4 pages, 3 figures, accepted for publication in Physical Review Letter

El perfil afectivo/matemático de estudiantes de ciencias e ingeniería

En la investigación en educación matemática, el rendimiento se ha estudiado desde diferentes ópticas: cognitiva, social y emocional, entre otras. Este estudio analiza las creencias y actitudes de estudiantes de ingeniería y de ciencias a través de una metodología basada en la lógica fuzzy. Los resultados muestran, que a los de ingeniería les gustan más las matemáticas, presentan mayor autoestima matemática y creen que las matemáticas son importantes de un modo significativamente mayor que para los estudiantes de ciencias. No obstante, todos son conscientes de su responsabilidad en el aprendizaje de las matemáticas, y coinciden en valorar el papel del profesor, aunque no se considere un elemento influyente a nivel emocional

Biaxial Strain in the Hexagonal Plane of MnAs Thin Films: The Key to Stabilize Ferromagnetism to Higher Temperature

The alpha-beta magneto-structural phase transition in MnAs/GaAs(111) epilayers is investigated by elastic neutron scattering. The in-plane parameter of MnAs remains almost constant with temperature from 100 K to 420 K, following the thermal evolution of the GaAs substrate. This induces a temperature dependent biaxial strain that is responsible for an alpha-beta phase coexistence and, more important, for the stabilization of the ferromagnetic alpha-phase at higher temperature than in bulk. We explain the premature appearance of the beta-phase at 275 K and the persistence of the ferromagnetic alpha-phase up to 350 K with thermodynamical arguments based on the MnAs phase diagram. It results that the biaxial strain in the hexagonal plane is the key parameter to extend the ferromagnetic phase well over room temperature.Comment: 4 pages, 3 figures, accepted for publication in Physical Review Letter

Effects of critical temperature inhomogeneities on the voltage-current characteristics of a planar superconductor near the Berezinskii-Kosterlitz-Thouless transition

We analyze numerically how the voltage-current (V-I) characteristics near the so-called Berezinskii-Kosterlitz-Thouless (BKT) transition of 2D superconductors are affected by a random spatial Gaussian distribution of critical temperature inhomogeneities with long characteristic lengths (much larger than the in-plane superconducting coherence length amplitude). Our simulations allow to quantify the broadening around the average BKT transition temperature of both the exponent alpha in V I^alpha and of the resistance V/I. These calculations reveal that strong spatial redistributions of the local current will occur around the transition as either I or the temperature T are varied. Our results also support that the condition alpha=3 provides a good estimate for the location of the average BKT transition temperature, and that extrapolating to alpha->1 the alpha(T) behaviour well below the transition provides a good estimate for the average mean-field critical temperature.Comment: 18 pages; pdfLaTeX; 1 TeX file + 8 PDF files for figures (figs.1,2,3a,3b,4,5a,5b,6

Electromagnetic dipole moments of charged baryons with bent crystals at the LHC

We propose a unique program of measurements of electric and magnetic dipole moments of charm, beauty and strange charged baryons at the LHC, based on the phenomenon of spin precession of channeled particles in bent crystals. Studies of crystal channeling and spin precession of positively- and negatively-charged particles are presented, along with feasibility studies and expected sensitivities for the proposed experiment using a layout based on the LHCb detector.Comment: 19 pages, 13 figure

Dynamics of entanglement of bosonic modes on symmetric graphs

We investigate the dynamics of an initially disentangled Gaussian state on a general finite symmetric graph. As concrete examples we obtain properties of this dynamics on mean field graphs of arbitrary sizes. In the same way that chains can be used for transmitting entanglement by their natural dynamics, these graphs can be used to store entanglement. We also consider two kinds of regular polyhedron which show interesting features of entanglement sharing.Comment: 14 pages, 11 figures, Accepted for publication in Physics Letters