Traditional Landau-Ginzburg-Wilson paradigm has had great success in describing quantum phase transitions using an order parameter. However this approach does not allow a direct second order phase transitions between two phases with unrelated symmetries, such as one from a Néel ordered state to a valence bond solid (VBS) state, unless fine-tuned. Deconfined quantum criticality is characterized by an emergent gauge field that couples to fractionalized particles. Such theory can describe a direct Néel to VBS phase transition.
We show that the Néel states of two-dimensional antiferromagnets have low energy vector boson excitations in the vicinity of deconfined quantum critical points. We compute the universal damping of these excitations arising from spin-wave emission. Detection of such a vector boson will demonstrate the existence of emergent topological gauge excitations in a quantum spin system.
 Y. Huh, P. Strack, and S. Sachdev, Phys. Rev. Lett. 111, 166401 (2013)
 Y. Huh, P. Strack, and S. Sachdev, Phys. Rev. B. 88, 155109 (2013)