Broken orientational and reflection symmetries in thin film superconductors with mesoscopic magnetic dipoles

Within Ginzburg-Landau theory, we study vortex configurations in periodic nanoscale superconducting dot arrays with ferromagnetic inclusions. The magnetic moments of the dipoles are oriented out of the plane, and no external flux is applied. We find that sufficiently strong dipoles induce the formation of vortex-antivortex pairs with the vortices usually confined in the dot regions and the antivortices forming a lattice in the interstitial areas. The vortex-antivortex pair density exhibits broad plateaus as a function of the dot dipole moment. Although in most cases, the number of antivortices per unit cell is integral, we have identified a half-integral plateau in which some antivortices are shared by two magnetic dots. Many of the plateaus correspond to vortex configurations which break lattice symmetries. Some of these configurations involve the marked deformation of vortex cores. Experimental implications of these novel results are discussed. (C) 2004 Elsevier B.V. All rights reserved.