Transport Behavior Of Vortices With Square Periodic Pinning Array

If a current traverses in high temperature superconductor in mixed state, vortices will move under the driving force caused by the current. Because pins in superconductor can block the moving of vortex, high current transmission with non-resistance can be achieved theoretically. To achieve non-resistance current transmission, many interesting phenomena were discovered in the field of vortex dynamics.Along with the development of vortex dynamics, people discovered the transport in two perpendicular directions is isotropic for all disordered pining arrays and most rectangular,triangle and honeycomb periodic pinning arrays. Anisotropy transport behaviors were also found for specific anisotropic pinning arrays. In this thesis we will study the transport behavior of two-dimensional vortices with square periodic pinning arrays.In the first chapter of the thesis, we introduce the vortex properties, phase diagram of vortex system, and the isotropic and anisotropic transport behaviors of high temperature superconductor. In the second chapter, we describe the physical model of vortex and pinning that we used in our numerical simulations. Also, we introduce the numerical method-Molecular Dynamic Method. In the third chapter, we show that the transport behavior in x-direction and y-direction of square periodic pinning arrays at 0K and the 4th matching field. We observe the transport behaviors along both directions are the same. It attributes to the re-configuration of vortex arrays occurring before the critical depining force Fc. After that, the two configurations are the same along the both direction. In the last chapter, we discuss the impact of temperature, pinning density, and finite size effect. The depining force Fc becomes lower with the increase in the temperature. We present the dynamical phase diagram of vortices, and we find four different phases:one pinning phase, two channel flow phases, and one smectic phase. In channel flowâ… phase a small portion of interstitial vortices are pinned while all interstitial vortices move in channel flowâ…¡phase. And channel flowâ…¡phase die away with the increase in pinning density.