Study of size effects in critical currents and dynamical behavior of vortices in type ii superconducting strips with periodic pinning at finite temperature.

Abstract

In the present work we propose the study of critical currents and dynamical behavior of vortices in type II Superconducting stripes with Kagomé and hexagonal arrays of pinning centers. In addition to the finite geometry and pinning effects, the system behavior when external parameters such as temperature and magnetic field are changed will be analyzed. When the transport current J exceeds a critical value, the vortices starts to move and dissipate energy. One of the most important mechanisms used to increase the critical current in type II superconductors is the vortex pinning. A great experimental effort has been made to increase the pinning effects creating structural defects. However, the pinning mechanism has not been completely understood, and theoretical studies could help to comprehend the pinning influence in critical currents and dynamical behavior. Our system corresponds to a bi-dimensional superconductor, finite in transversal and infinite in longitudinal direction. The description of the vortex system is made using a set of Langevin equations, and the Molecular Dynamics Technique is used to simulate the vortex dynamics. The solution of these equations will provide the vortex trajectories and velocities. With the trajectories is possible to characterize the dynamical phases and with the velocities the value of critical current. Others physical quantities as differential resistance, transversal diffusion coefficient and structure factor will be calculated to obtain a better characterization of the system dynamics. A detailed comparison with infinite superconducting thin films with Kagomé and hexagonal pinning arrays will be made, helping to achieve a better understanding of the size effects. The understanding of pinning mechanism and size effects at finite temperature is important because provides a better description of superconductors used in real applications. Moreover, the development of this project could help in the discovery of new superconducting materials with higher efficiency for technological uses. (AU)