| In this dissertation, we present a theoretical study of artificially fabricated Josephson junction array systems. The work is an attempt to understand the vortex structure of the system using various types of computer simulation, including Monte Carlo and Langevin dynamics.; In chapter 1, we present a brief introduction to Josephson junction arrays, as well as to high temperature superconductors, and we discuss why they may be related to each other in certain physical circumstances.; In chapter 2, we present two models used in later chapters. The resistively capacitively shunted junction model can be used to study the dynamics of the Josephson junction arrays, including both equilibrium and non-equilibrium properties. The XY model is used to study the equilibrium properties and phase transitions of the system.; In chapter 4, we show that vortices may be screened out of a Josephson junction ladder even though the magnetic flux itself is not screened out. The dynamical ground state of the ladder is numerically probed with applied external current applied both perpendicular and parallel to the ladder edges. We find that the screening of vortex number occurs in the perpendicular case but not in the parallel case.; In chapter 3, we study the first order melting phase transition of a flux line lattice melting in a simple cubic with a magnetic field applied in (111) direction. At high diagonal magnetic field, the flux line lattice melting is accompanied by the simultaneous loss of phase coherence in the planes perpendicular and parallel to the magnetic field direction at the same temperature. The first order melting of the flux line lattice which we observe is similar to what is seen experimentally in high temperature superconductors.; In chapter 5, we study the vortex dynamics in two dimensional Josephson junction arrays. We present a picture of the vortex-antivortex unbinding transition and the flux line lattice melting in two dimensional system. In particular, we calculate the flux noise and fluctuation conductivity. Both quantities show clear critical slowing down and remarkable scaling behaviors.; Finally, in chapter 6, we present brief conclusions and possible extensions for the future. |
