Eur. Phys. J. B 7, 211-218 (1999)
https://doi.org/10.1007/s100510050606

Van der Waals interaction between flux lines in high-T_c superconductors: A variational approach

¹ Universität zu Köln, Institut für theoretische Physik, Zülpicher Str. 77, 50937 Köln, Germany
² Tel Aviv University, The Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics and Astronomy, 69978 Tel Aviv, Israel

Received: 25 June 1996
Revised: 18 August 1998
Accepted: 21 August 1998
Published online: 15 January 1999

Abstract

In pure anisotropic or layered superconductors thermal fluctuations induce a van der Waals attraction between flux lines. This attraction together with the entropic repulsion has interesting consequences for the low field phase diagram; in particular, a first order transition from the Meissner phase to the mixed state is induced. We introduce a new variational approach that allows for the calculation of the effective free energy of the flux line lattice on the scale of the mean flux line distance a, which is based on an expansion of the free energy around the regular triangular Abrikosov lattice. Using this technique, the low field phase diagram of these materials may be explored. The results of this technique are compared with a recent functional RG treatment of the same system.