UNCONVENTIONAL QUANTUM CRITICAL POINTS

In this paper we review the theory of unconventional quantum critical points that are beyond the Landau's paradigm. Three types of unconventional QCPs will be discussed: (1) The transition between topological order and semiclassical spin ordered phase; (2) The transition between topological order and valence bond solid phase; (3) The direct second order transition between different competing orders. We focus on the field theory and universality class of these unconventional QCPs. Relation of these QCPs with recent numerical simulations and experiments on quantum frustrated magnets are also discussed.