Point defects in the flux-line lattice of superconductors

The self-energy and interaction energy of vacancies and interstitials in the triangular lattice of parallel Abrikosov vortices in type-II superconductors are calculated within London theory. Various stable and metastable equilibrium configurations of the flux-line lattice around such point defects are investigated. The vacancy with highest (sixfold) symmetry usually does not exhibit the lowest energy, as was already found by Frey et al. [Phys. Rev. B 49, 9723 (1994)]. Due to the relaxation of the surrounding vortex lattice, the defect energies are very small compared with the binding energy of one vortex. The interaction of point defects is weak and can be repulsive or attractive, depending on their type and distance and on the ratio of the magnetic penetration depth $\ensuremath{\lambda}$ to the average vortex spacing $a$. In the limit $\ensuremath{\lambda}\ensuremath{\gg}a$ these results should be applicable to thin films in a perpendicular magnetic field.