Vortex lattice structures in uniaxial superconductors

Abstract

The structure of the vortex lattice in anisotropic, unaxial superconductors in the domain Hc1≪H≪Hc2 is considered within the London approach. To first order in the small parameter (Lλ)2, where L is the average intervortex spacing and λ is the average penetration depth, there exists a continuum of different lattices with the same free energy for any direction of the magnetic induction B with respect to the crystal. It is shown that the degeneracy is removed if terms in the free energy of order (Lλ)4 are taken into account, yielding both a unique structure and a preferred orientation of the vortex lattice with respect to the direction of B within the crystal. Parameters of the primitive cell for this structure are obtained and evaluated for known values of the anisotropy of YBa2Cu3O7. For the particular case of vortices parallel to the Cu-O planes the degeneracy remains exact (within the London approach), which should make this lattice more susceptible to disorder. The magnetization is shown to be almost parallel to the c^ crystal direction for all orientations of the external field H0, except in a narrow domain where H0 is nearly normal to c^.

Source-reported materials — not catalogue approval

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