The Phase Transition to a Square Vortex Lattice in Type-II Superconductors with Fourfold Anisotropy

Abstract

We investigate the stability of the square vortex lattice which has been recently observed in experiments on the borocarbide family of superconductors. Taking into account the tetragonal symmetry of these systems, we add fourfold symmetric fourth-derivative terms to the Ginzburg-Landau(GL) free energy. At $H_{c2}$ these terms may be treated perturbatively to lowest order to locate the transition from a distorted hexagonal to a square vortex lattice. We also solve for this phase boundary numerically in the strongly type-II limit, finding large corrections to the lowest-order perturbative results. We calculate the relative fourfold $H_{c2}$ anisotropy for field in the $xy$ plane to be 4.5% at the temperature, $T_c^{\square }$, where the transition occurs at $H_{c2}$ for field along the $z$ axis. This is to be compared to the 3.6% obtained in the perturbative calculation. Furthermore, we find that the phase boundary in the $H-T$ phase diagram has positive slope near $H_{c2}$.

15 pages including 2 figures, LaTex

References in corpus (1)

• Generalized London free energy for high-$T_c$ vortex lattices

Cited by in corpus (8)

• Ginzburg-Landau theory of vortices in a multi-gap superconductor
• The Ginzburg-Landau Theory of Type II superconductors in magnetic field
• Ginzburg-Landau Theory for a p-Wave Sr_2RuO_4 Superconductor: Vortex Core Structure and Extended London Theory
• Vortex Lattice Structural Transitions: a Ginzburg-Landau Model Approach
• Structural Transitions in Vortex Systems with Anisotropic Interactions
• First-Order Reorientation of the Flux-Line Lattice in CaAlSi
• Rotational transition, domain formation, dislocations and defects in vortex systems with combined six- and 12-fold anisotropic interactions
• The puzzle of 90 degree reorientation in the vortex lattice of borocarbide superconductors