Flux Lattices in the High T sub c Superconductors

I will discuss two types of experiments which provide information about the statics and dynamics of flux lattices in YBa sub 2 Cu sub 3 O sub 7. The first are magnetic decoration experiments in which the flux lines are decorated with amgnetic particles. From these experiments we have learned that the flux lattice is triangular with the normal value for the flux quantum. In ultrasound and high Q mechanical oscillator experiments we have looked at flux lattice melting. These experiments show that the flux lattices melts well below Hc sub 2 into a vortex liquid state. These results suggest that the vortex solid and its melting is essentially two-dimensional in character. Inb addition I will discuss mechanical melting experiments in true 2 sup D systems and in heavy fermion superconductors.