Eigenschaften der L�sungen der nichtlinearisierten Ginsburg-Landau-Gleichungen in Zylindersymmetrie

Abstract

Solutions of the nonlinear Ginzburg-Landau equations in cylindrical symmetry have been computed for a type I superconductor. From these solutions the behaviour of a circular cylinder of infinite length in a magnetic field parallel to its axis has been deduced. For a series of values of the magnetic field solutions are given in two cases. The first case was calculated with the assumption of no fluxoid frozen in (fluxoid quantum number n=0), whereas in the second case a vortex with fluxoid quantum numbern=1 was assumed on the axis of the cylinder. For both series of solutions investigation of the thermodynamic stability was carried out. This and further thermodynamic considerations led to the result that in a gedankenexperiment the transition from the normal to the superconducting state and vice versa can be performed in a reversible manner. The expulsion of the magnetic field from the sample during the reversible transition to the superconducting state (Meissner-Effect) is also described by the solutions. Further results are the existence of a supercooled state down to a magnetic fieldHc2=κ√2Hcb and of a superheated state up to a fieldHc1>Hcb. The value ofHc1 depends on the radius of the cylinder. If a condensation to the superconducting state takes place at a fieldH0 whereHc2<H0<Hcb, condensation withn=0 seems to be preferred in comparison to that withn=1.