Melting of the flux line lattice

Since the recent discovery of the high-temperature superconductors, there have been many ideas put forward to explain the phase diagram. One of the most important parts of this phase diagram is the so called irreversible line. The majority opinion is that this line represents a phase transition from a flux line solid to a flux line fluid, that is a melting transition. The following is a brief review of some of the ideas put forward to explain this.