## 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 (Formula presented) 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 (Formula presented) anisotropy for field in the (Formula presented) plane to be 4.5% at the temperature, (Formula presented) where the transition occurs at (Formula presented) 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 (Formula presented) phase diagram has positive slope near (Formula presented).

Original language | English (US) |
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Pages (from-to) | 9427-9432 |

Number of pages | 6 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 58 |

Issue number | 14 |

DOIs | |

State | Published - 1998 |

## All Science Journal Classification (ASJC) codes

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics