Supercondutores mesoscópicos via teoria de Ginzburg-Landau

Abstract

In this thesis, we study the physical properties of superconducting materials such as magnetization, free energy, magnetic susceptibility, vorticity and vortex dynamics, using the time-dependent Ginzburg-Landau equations (TDGL), and the − U method to do the computer simulation in samples of one and two bands. At first, a sample with defects in the edges and the center was submitted to an external magnetic field from which the magnetization, free energy, the phase diagram, and the vortex dynamics were obtained. We can observe the decrease in the critical fields Hc1 and Hc2 with increasing temperature and that the central defect in the material influences the configuration of the vortex functioning as a vortex trapping center. On another occasion, we analyzed the behavior of a superconductor, in which the defects were filled with a superconducting material with Tc greater and submitted to a transport current. We obtained the critical current Jc 1 where we can see its inverse dependence with the increase in temperature, and the beginning of the resistive state with the appearance of a kinematic vortex-antivortex pair (V-Av). We found the resistivity with function of the applied current and its characteristic shape due to the ultra-fast movement of the vortices. We found a drastic decrease in the critical current Jc1, due to the application of an external magnetic field and the appearance of two Abrikosov vortices. Within the two-band formalism (2B-TDGL), we seek to understand how the vortexes behave in a square sample with a central defect. Here we find an interesting result: the configuration of the vortices does not obey Abrikosov’s triangular lattice due to the competition between the bands to maintain their superconducting state. As the defect increased, the sample became more diamagnetic as there was no change in the Hc2 field, where the central defect led to the anchoring of the vortexes. To simulate a situation in which the sample is in contact with other material, that is, the effects of interfacing with ferromagnetic or superconducting material with Tc greater, we use the influence of deGennes b extrapolation length. We observed an unconventional vortex state and a decrease in the Hc1 field, when the interface is ferromagnetic/superconducting and an increase when we have a superconducting/superconducting interface. This decrease/increase is due to contamination at the material boundaries by electrons/Cooper pairs that contribute to the degradation/increase of the superconducting state.