Quantum Phase Transitions in 2d Quantum Liquids
  These lectures provide a pedagogical introduction to the theory of continuous quantum phase transitions. Various two-dimensional condensed matter systems, such as a superconducting film, a quantum Hall liquid, and an array of Josephson junctions, undergo such a phase transition at the absolute zero of temperature. The universality classes defined by repulsively interacting bosons with and without disorder are shown to play a central role in understanding these systems. 
Adriaan M. J. Schakel (Freie Universitaet Berlin)