arXiv subjects

Isaías G. de Oliveira

Publications and source records attributed to Isaías G. de Oliveira.

4 recordsLinked to original sources

arXiv2026

Giant Resonances in Superconducting Films Induced by Nonsuperconducting Layers

We find that commensurate resonances in superconducting films endowed with a $SISIS$ structure, where $S$ and $I$ stand for superconducting and insulating layers, respectively, enhance the gap to a value three to four times the bulk gap. Such resonances rely on spatially localized quantum states that arise due to the commensurability between the total film thickness and the distance between the two insulating barriers. Our results are obtained in the context of the Bogoliubov-de Gennes equations within the Anderson approximation, applied here to Bi films, where quantum size effects are possible due to the abnormally large mean free path.

cond-mat.supr-con↗

arXiv2020

The intermediate type-I superconductors in the mesoscopic scale

M. Tinkham and P. G. de Gennes, described in their books the existence of an intermediate type-I superconductor as a consequence of an external surface that affects the well known classification of superconductors into type-I and II. Here we consider the mesoscopic superconductor where the ratio volume to area is small and the effects of the external surface are enhanced. By means of the standard Ginzburg-Landau theory the Tinkham-de Gennes scenario is extended to the mesoscopic type-I superconductor. We find new features of the transition at the passage from the genuine to the intermediate type-I. The latter has two distinct transitions, namely, from a paramagnetic to diamagnetic response in descending field and a quasi type-II behavior as the critical coupling is approached in ascending field. The intermediate type-I phase proposed here, and its corresponding transitions, reflect intrinsic features of the superconductor and not its geometrical properties.

cond-mat.supr-con↗

arXiv2017

The magnetocaloric effect from the point of view of Tsallis non-extensive thermostatistics

In this work we have analyzed the magnetocaloric effect (MCE) from the Tsallis thermostatistics formalism (TTF) point of view. The problem discussed here is a two level system MCE. We have calculated, both analytically and numerically, the entropy of this system as a function of the Tsallis' parameter (the well known q-parameter) which value depends on the extensivity (q<1) or non-extensivity (q>1) of the system. Since we consider this MCE not depending on the initial conditions, which classify our system as a non-extensive one, we used several greater than one q-parameters to understand the effect of the nonextensive formalism in the entropy as well as the magnetocaloric potential, $ΔS$. We have plotted several curves that shows precisely the behavior of this effect when dealt with non-extensive statistics.

physics.gen-ph↗

arXiv2012

Little-Parks oscillations near a persistent current loop

We investigate the Little-Parks oscillations caused by a persistent current loop set on the top edge of a mesoscopic superconducting thin-walled cylinder with a finite height. For a short cylinder the Little-Parks oscillations are approximately the same ones as the standard effect, as there is only one magnetic flux piercing the cylinder. For a tall cylinder the inhomogeneity of the magnetic field makes different magnetic fluxes pierce the cylinder at distinct heights and we show here that this produces two distinct Little-Parks oscillatory regimes according to the persistent current loop. We show that these two regimes, and also the transition between them, are observable in current measurements done in the superconducting cylinder. The two regimes stem from different behavior along the height, as seen in the order parameter, numerically obtained from the Ginzburg-Landau theory through the finite element method

cond-mat.supr-con↗