Two dimensional Josephson junction arrays

Two dimensional Josephson junction arrays (JJAs) offer the opportunity to study a variety of basic physical concepts. The present review focuses on recent experimental work on the dynamics of JJAs, as characterized by ac conductance measurements. The review starts with a discussion of basic physics necessary to describe JJAs. Some experimental issues, array fabrication and measurement techniques are considered next. In a perpendicular magnetic field, a JJA is an experimental realization of the frustrated XY model, with the frustration parameter f, corresponding to the number of flux: quanta in a unit cell of the array, adjusted by the magnetic field. It is thereby possible to investigate the nature of the ground states at arbitrary frustrations. Phase transitions are the next topic: the vortex unbinding transition is observed at integer f-values, while, if the junction coupling energies are appropriately varied across the array, at half-integer f-values the Ising transition, associated with chiral symmetry breaking, may be observed. Some aspects of vortex: dynamics, a subject which is not yet completely understood, are then considered. Under certain conditions there is virtually no pinning in JJAs, they are therefore ideally suited for the study of vortex dynamics. The next topic of this review is concerned with the influence of disorder on the ground states and on the phase transitions in JJAs. Site percolation in JJAs has provided some insights into the physics of disordered systems and allowed to verify some theoretical predictions on percolation in two dimensions. A quick look at JJAs in the underdamped regime concludes this review.