Numerical study of vortices in a two-dimensional XY model with in-plane magnetic field

Many physical systems of interest can be mapped into the planar rotator and XY magnetic models with a magnetic field applied within the easy plane. In this work we study how the shape and energy of a vortex-antivortex pair depends on the applied field and on the pair separation. Our results show a new feature: the energy related to the vortex-antivortex pair has a coefficient which depends strongly on the applied field. For large separation of the pair, the energy increases roughly with the square root of the field and linearly with the pair separation.