Ferromagnetic Annulus And Superconducting Vortices

The screening currents induced in a superconducting film by a magnetic annulus whose magnetization is perpendicular to the superconductor are calculated. We show that close to the superconductor transition temperature $T_c$ particular values of the magnetization and radii of the annulus make the creation of superconducting vortices energy favorable. We also show that the magnetic annulus offers an alternative tool for vortex pinning in the superconductor. Statistical mechanical properties of this system are discussed.Comment: 4 pages, 2 figures, submitted to PR

Symmetry Violation in a Superconducting Film with a Square Array of Ferromagnetic Dots

We study the equilibrium state of a superconducting film covered with a regular square array of perpendicularly magnetized magnetic dots. The dots induce vortices in the film directly under them and antivortices between the dots. We show that the symmetry of the dot array is spontaneously violated by the vortices. The positions of the vortices and the antivortices depend on the magnetization and the size of the dots.Comment: 6 pages, 3 figure

Diffusion in a strongly correlated anisotropic overlayer

We study the collective diffusion in chain structures on anisotropic substrates like (112) bcc and (110) fcc surfaces with deep troughs in the substrate potential corrugation. These chain structures are aligned normal to the troughs and can move only along the troughs. In a combination of theoretical arguments and of numerical simulations, we study the mass transport in these anisotropic systems. We find that a mechanism similar to soliton diffusion, instead of single particle diffusion, is still effective at temperatures well above the melting temperature of the ordered chain structures. This mechanism is directly correlated with the ordered phases that appear at much lower temperatures. As a consequence, also the influence of frozen disorder is still visible above the melting temperature. Theoretically we predict a strong dependence of the pre-exponential factor and weak dependence of the activation energy on the concentration of frozen surface defects. These predictions are confirmed by the simulations.Comment: Latex file, 18 pages and 9 eps figures include

Field theory of bi- and tetracritical points: Relaxational dynamics

We calculate the relaxational dynamical critical behavior of systems of $O(n_\|)\oplus O(n_\perp)$ symmetry by renormalization group method within the minimal subtraction scheme in two loop order. The three different bicritical static universality classes previously found for such systems correspond to three different dynamical universality classes within the static borderlines. The Heisenberg and the biconical fixed point lead to strong dynamic scaling whereas in the region of stability of the decoupled fixed point weak dynamic scaling holds. Due to the neighborhood of the stability border between the strong and the weak scaling dynamic fixed point corresponding to the static biconical and the decoupled fixed point a very small dynamic transient exponent, of $\omega_v^{{\cal B}}=0.0044$, is present in the dynamics for the physically important case $n_\|=1$ and $n_\perp=2$ in $d=3$.Comment: 8 figure