Voltage Noise And Driven Dynamics Of Current-Driven Vortices In Disordered Josephson

In recent years much theoretical and experimental effort has been made to study the dynamic phenomena of vortex motion driven by an external current in type-II superconductors. Many complex dynamic phenomena in the vortex system arise from a competition between spontaneously periodic structures of interacting vortices and disordered factors. Since the ceramic superconductors, especially in their polycrystalline form, behave in many respects like a random arrangement of weak links between superconducting grains. Thus a discrete lattice structure of two-dimensional (2D) Josephson junction arrays (JJAS), with controlled disorder and controlled Josephson coupling, may shed light on such layered superconductors or film materials. In this dissertation, based on RSJ model and by means of Runge-Kutta numerical simulation methods, dynamical phenomena of moving vortices and voltage noise spectra are studied in disordered Josephson junction arrays. The main results are listed as follows:(1) Using a numerical simulation, we have investigated the threshold currents, voltage–voltage correlation and current-driven dynamics of vortex systems in the disordered JJAS under a magnetic field. For the weak disorder, the depinning of the vortex lattice is driven by elastic deformation, and plastic deformation does not occur dominantly. For the strong disorder, vortex–antivortex pairs are excited prior to the depinning of vortex lattices. Depending on the strength of the disorder, the plastic flow (deformation) of vortex lattices or the nucleation of vortex–antivortex pairs occurs at a certain critical current.(2) For the strong disorder, we study the dynamic melting transition (DMT) driven by current in the vortex lattices. By calculating the voltage drop across the array, the vorticity due to the excitation of vortex and antivortex pairs (VAPS), and the voltage noise spectra of the moving vortices, we study the dynamical phenomena and DMT of moving vortices in disordered JJAS, and propose some innovative viewpoints. We first propose two dynamic melting transitions driven by current: one is at Ipto...