Spontaneous interlayer exciton coherence in quantum Hall bilayers at v=1 and v=2: a tutorial

This tutorial paper reviews some of the physics of quantum Hall bilayers with a focus on the case where there is low or zero tunnelling between the two layers. We describe the interlayer coherent states at filling factors v=1 and v=2 as exciton condensates and discuss some of the theory associated with these states.