Regensburg 2013 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 45: Superconductivity: (General) Theory
TT 45.6: Talk
Wednesday, March 13, 2013, 16:15–16:30, H21
Stability of super-currents and condensates in type I superconductors — •Klaus Morawetz1,2,3, Pavel Lipavsky4, Bretislav Sopik4, and Michael Maennel1 — 1Münster University of Applied Sciences, Stegerwaldstrasse 39, 48565 Steinfurt, Germany — 2International Institute of Physics (IIP), Av. Odilon Gomes de Lima 1722, 59078-400 Natal, Brazil — 3Max-Planck-Institute for the Physics of Complex Systems, 01187 Dresden, Germany — 4Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 12116 Prague 2, Czech Republic
Excitations of Cooper pairs into non-condensed bound pairs are similar to excitations of true bosons out of the Bose-Einstein condensate. Using the Landau criterion of superfluidity we evaluate the critical current above which these pair-excitations would lead to a finite resistivity. The predicted value strongly depends on the chosen approximation. The Kadanoff-Martin theory which is in many aspects equivalent to the BCS theory, leads to zero critical velocity, what is in conflict with the mere existence of super-currents. In contrast, the T-matrix with multiple scattering corrections provides the critical velocity of pair excitation which is √3-times larger than the critical velocity of pair breaking. This agrees with the experimentally well established fact that super-currents in type I superconductors are limited by pair breaking, not by pair excitation.