Vortex matter and its phase transitions

The mixed state of type II superconductors has magnetic flux penetrating th e sample in the form of vortices, with each vortex carrying an identical qu antum of flux. These vortices generally form a triangular lattice under wea k mutually repulsive forces; the lattice spacing can be easily varied over many orders of magnitude by varying the external magnetic field. The elasti c moduli of this lattice are small and this soft vortex matter can undergo phase transitions like normal matter, but with thermal fluctuations and und erlying defects playing an important role. We discuss experimental studies on vortex matter phase transitions, with some emphasis on DC magnetization measurements investigating the nature of the phase transition.