Enhanced thermal Hall effect in the square-lattice Neel state

Common wisdom about conventional antiferromagnets is that their low-energy physics is governed by spin-wave excitations. However, recent experiments on several cuprate compounds have challenged this concept. An enhanced thermal Hall response in the pseudogap phase was identified, which persists even in the insulating parent compounds without doping. Here, to explain these surprising observations, we study the quantum phase transition of a square-lattice antiferromagnet from a confining Neel state to a state with coexisting Neel and semion topological order. The transition is driven by an applied magnetic field and involves no change in the symmetry of the state. The critical point is described by a strongly coupled conformal field theory with an emergent global SO(3) symmetry. The field theory has four different formulations in terms of SU(2) or U(1) gauge theories, which are all related by dualities; we relate all four theories to the lattice degrees of freedom. We show how proximity of the confining Neel state to the critical point can explain the enhanced thermal Hall effect seen in experiments.