Nature of the 45 degrees vortex lattice reorientation in tetragonal superconductors

Abstract

The transformation of the vortex lattice in a tetragonal superconductor which consists of the 45 degrees reorientation relative to the crystal axes is studied using the nonlocal London model. It is shown that the reorientation occurs as two successive second order (continuous) phase transitions. The transition magnetic fields are calculated for a range of parameters relevant for borocarbide superconductors in which the reorientation has been observed.