Holographic Description of Finite Size Effects in Strongly Coupled Superconductors

Despite its fundamental and practical interest, the understanding of mesoscopic effects in strongly coupled superconductors is still limited. Here we address this problem by studying holographic superconductivity in a disk and a strip of typical size $\ell$. For $\ell < \ell_c$, where $\ell_c$ depends on the chemical potential and temperature, we have found that the order parameter vanishes. The superconductor-metal transition at $\ell = \ell_c$ is controlled by mean-field critical exponents which suggests that quantum and thermal fluctuations induced by finite size effects are suppressed in holographic superconductors. Intriguingly, the effective interactions that bind the order parameter increases as $\ell$ decreases. Most of these results are consistent with experimental observations in Pb nanograins at low temperature and qualitatively different from the ones expected in a weakly coupled superconductor.Comment: 4 pages, 3 figure

Influence of the strong metal support interaction effect (SMSI) of Pt/TiO2 and Pd/TiO2 systems in the photocatalytic biohydrogen production from glucose solution

Two different catalysts consisting of Pt/TiO2 and Pd/TiO 2 were submitted to diverse oxidative and reductive calcination treatments and tested for photocatalytic reforming of glucose water solution (as a model of biomass component) in H2 production. Oxidation and reduction at 850°C resulted in better photocatalysts for hydrogen production than Degussa P-25 and the ones prepared at 500°C, despite the fact that the former consisted in very low surface area (6-8 m2/g) rutile titania specimens. The platinum-containing systems prepared at 850°C give the most effective catalysts. XPS characterization of the systems showed that thermal treatment at 850°C resulted in electron transfer from titania to metal particles through the so-called strong metal-support interaction (SMSI) effect. Furthermore, the greater the SMSI effect, the better the catalytic performance. Improvement in photocatalytic behavior is explained in terms of avoidance of electron-hole recombination through the electron transfer from titania to metal particles

Improvement of the ultra-trace voltammetric determination of Rh in environmental samples using signal transformation

En prensa3,498

Origin of anomalous breakdown of Bloch's rule in the Mott-Hubbard insulator MnTe2_2

We reinvestigate the pressure dependence of the crystal structure and antiferromagnetic phase transition in MnTe$_2$ by the rigorous and reliable tool of high pressure neutron powder diffraction. First-principles density functional theory calculations are carried out in order to gain microscopic insight. The measured N\'eel temperature of MnTe$_2$ is found to show unusually large pressure dependence of $12$ K GPa$^{-1}$. This gives rise to large violation of Bloch's rule given by $\alpha=\frac{d\log T_N}{d\log V}=-\frac{10}{3} \approx -3.3$, to a $\alpha$ value of -6.0 $\pm$ 0.1 for MnTe$_2$. The ab-initio calculation of the electronic structure and the magnetic exchange interactions in MnTe$_2$, for the measured crystal structures at different pressures, gives the pressure dependence of the Ne\'el temperature, $\alpha$ to be -5.61, in close agreement with experimental finding. The microscopic origin of this behavior turns to be dictated by the distance dependence of the cation-anion hopping interaction strength