The glass transition in high-temperature superconductors

Abstract: In high-temperature superconductors a large region of the magnetic phase diagram is occupied by a vortex phase. This vortex phase can be divided into two regions. At lower temperatures the vortices are in a truly superconducting solid phase. At higher temperatures the solid changes to a dissipative vortex liquid. The transition between the two phases depends of the disorder in the material. If there is no or low disorder the transition is a first order transition but if there are a lot of disorder the vortex solid is called a vortex glass and the transition is a second order transition. To describe this theoretically there are two kinds of models. First introduced was the so called vortex glass model with its characteristics of diverging time and length scales. Later was thevortex molasses scenario introduced, where only a diverging time scale can be observed. The task of this thesis is to try to distinguish between the two kinds of models. This was carried out by sensitive R(T) measurements. The experiment was based on single crystals of YBa2Cu3O7-(YBCO). An unambiguous result could not be obtained, further  experiments would have to be conducted to make definite conclusions.