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Dependence of the Energy Gap in Superconductors on Position and Magnetic Field

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1 Author(s)
Tinkham, M. ; Department of Physics, University of California, Berkeley, USA

A review is given of work concerning the decrease of the energy gap in superconductors when a magnetic field is applied. The absence of any observable effect in previous spectroscopic work is explained, and conditions for large effects are outlined. Experimental measurements on thermal conductivity and microwave absorption in films in a magnetic field are described. The results show that in thin films, the gap can be depressed continuously to zero, yielding a second-order phase transition. In thicker films, the gap can be only partially depressed before the transition, and the transition is of first order. These results agree with those obtained theoretically by Douglass from the Ginzburg-Landau-Gor'kov theory, and experimentally, by electron tunnelling. An attempt to generalize the Ginzburg-Landau-Gor'kov theory to cope with the case when ε0/kT ≫ 1 is then indicated. In this phenomenological theory, the normalized gap ε(H)/ε(0) is taken as an order parameter ω, and the free energy is assumed to contain a term in ξ02 |∇ω|2 , as well as a free energy density f(ω) and magnetic energy κ(ω)H2. Some success is found.

Note: The Institute of Electrical and Electronics Engineers, Incorporated is distributing this Article with permission of the International Business Machines Corporation (IBM) who is the exclusive owner. The recipient of this Article may not assign, sublicense, lease, rent or otherwise transfer, reproduce, prepare derivative works, publicly display or perform, or distribute the Article.  

Published in:

IBM Journal of Research and Development  (Volume:6 ,  Issue: 1 )