The superconducting-insulator transition is simulated in disordered networks of Josephson junctions with thermally activated Arrhenius-like resistive shunt. By solving the conductance matrix of the network, the transition is reproduced in different experimental conditions by tuning thickness, charge density and disorder degree. In particular, on increasing fluctuations of the parameters entering the Josephson coupling and the Coulomb energy of the junctions, the transition occurs for decreasing values of the critical temperature Tc and increasing values of the activation temperature To. The results of the simulation compare well with recent experiments where the mesoscopic fluctuations of the phase have been suggested as the mechanism underlying the phenomenon of emergent granularity in otherwise homogeneous films. The proposed approach is compared with the results obtained on TiN films and nanopatterned arrays of weak-links, where the superconductor-insulator transition is directly stimulated. arXiv: 1304.1911v1 [cond-mat.supr-con]
In previous papers (Mazzetti et al. in Phys. Rev. B 77:064516, 2008; Ponta et al. in Phys. Rev. B 79:134513, 2009) the mechanism of resistive transition of MgB2 films has been investigated by the analysis of the non-stationary noise produced during the transition process. The developed model suggested that when the transition occurs very near to T (C) at low bias current, a mixed state, consisting of normal and superconductive domains, takes place. A different model based on fluxoids dynamics, generated by the current and/or by an external field, is appropriate when the transition occurs at strong bias currents and temperatures much lower than T (C). The purpose of this paper is a further investigation of the transition process at low bias currents by analyzing the 1/f power spectra of the noise, taken in stationary conditions at different values of the specimen resistance. These spectra, when renormalized to represent the relative fluctuation of the specimen resistance, are practically coincident, a fact in agreement with the developed model
LAMOST J202629.80+423652.0 has been recently classified as a new symbiotic star containing a long-period Mira, surrounded by dust (Dtype) and displaying in the optical spectra high ionization emission lines, including the Raman-scattered OVI at 6825 Å. We have observed LAMOST J202629.80+423652.0 photometrically in the BVRI bands and spectroscopically over the 3500-8000 Å range. We have found it to be a normal G8 IV sub-giant star, deprived of any emission line in its spectrum, and reddened by EB−V =0.35 mag. Combining our photometry with data from all-sky patrol surveys, we find LAMOST J202629.80+423652.0 to be non variable, so not pulsating as a Mira. We have compiled from existing sources its spectral energy distribution, extending well into the mid-Infrared, and found it completely dominated by the G8 IV photospheric stellar emission, without any sign of circumstellar dust. We therefore conclude that LAMOST J202629.80+423652.0 is not a symbiotic star, nor it is pulsating or been enshrouded in dust.
The resistive transition of polycrystalline superconducting MgB2 films is studied by means of an extensive set of stationary noise measurements, going from the very beginning of the transition to its final point, where the normal state is reached, either with and without magnetic field. The experimental results, taken at low current density and close to the critical temperature Tc, show very clearly the existence of two different dissipative processes at the different stages of the transition. An extended analysis proves that, at the beginning of the transition, when the resistance is below ten percent of normal value, the specimen is in a mixed state and dissipation is produced by fluxoid creation and motion. At higher temperature the specimen is in an intermediate state, constituted by a structure of interleaved superconducting and resistive domains. Such a situation occurs in type II superconductor when the transition temperature is very near to Tc and the critical field Hc for fluxoid penetration tends to zero. It is found that in the intermediate state, the power spectrum of the relative resistance fluctuations, is independent of the average resistance value and is unaffected by the magnetic field. As shown in the paper, this means that the noise is generated by density fluctuation of the normal electron gas in the resistive domains, while the contribution of the superconducting ones is negligible. The reduced noise amplitude does not depend on the steepness of the transition curve, thus adding further evidence to the above interpretation. The noise is thus related to the film impurities and can be investigated when the specimen is in the normal state, even at room temperature. The occurrence of a different dissipative process at low resistance is clearly evidenced by the experimental results, which show that the amplitude of the reduced power spectrum of the noise depends on magnetic field and resistance. These results are consistent with the assumption of fluxoid noise as shown by the model for the calculation of the noise developed in the manuscript.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.