The magnetic properties of small-K superconducting In-Bi, In-Tl, In-Pb, Sn-Bi, and Sn-Sb alloys are investigated. The evaluation of the experiments is carried out in the framework of BCS and GLAG theory. At a critical alloy concentration a phase transition occurs, at which type I superconductivity goes over into type II. Comparing the results with Lifshitz's theory, it is found that the phase transition is of higher than second order. The contribution from the nonanalytical part of the concentration dependence of the electronic specific heat coefficient is 0.63-0.77, and thus the order of the phase transition increases by this amount.
Macroscopic magnetic measurements were performed on superconducting alloys. From the results of these experiments microscopic parameters namely the energy gap and the vortex creation energy could be calculated. Their dependence on the additive material content (or on the GL-parameter) was determined. It was shown that the BCS and the GLAG theory are applicable for small-x superconductors in wide temperature interval.
Analytical expressions are givcn which describe the dependence of the critieal temperature, of the critical magnetic fields and of the GL parameter on the coneentration of the alloying material, eharacterizing the phase transition within the superconducting state in good agreement with the experiments.In one of our previous papers [1] it was diseovered that in supereondueting alloys of small GL parameter ~ a specifie phase transition of new type occurs on the effect of increasing alloy eoncentration. This means that having reached a certain critical concentration C c the previous type I supereonductivity (Meissner's state) goes over to type II (mixed state).Our experiments have been carried out with In-Bi specimens eontaining 0--5 at. % Bi [21.The evaluation of the experimental results shows that this phase transition occurs at any temperature-dependent ~(T) and at any temperature always whenever the value ~ = 1/V2=xc has been reached. Therefore this is eonsidered to be the critical value of GL parameter.The occurring phase transition can be characterized with the following fundamental features:1. The order parameter describing the supereonduetivity beeomes inhomogeneous as superconductive and normal domains appear. (In the presence of ah external current it becomes anisotropic as well). The vector potential has a similar behaviour too.2. The superconductivity, being previously a surface phenomenon, becomes a volumetric one. (The transport eurrent and the external magnetic field penetrate into the sample).3. Instead of one critical magnetic field H c describing the pure superconductivity the critical fields He1 and He2 together determine the magnetic p enetration. 4. A sudden change oceurs in the value of the thermodynamie entropy matrix [3]. 5. A quick ehange oceurs in the macroscopic conductivity matrix. (This registers the superconduetive-normal lattice structure).
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.