Anomalous symmetry breaking in an insulating cuprate

The phase diagram of the cuprates features many exotic states at finite doping including the pseudogap, strange metal and high-T_c superconducting states. However, it is generally believed that the un-doped parent system is a well understood Mott insulator, whose low energy physics is fully captured by a two-dimensional spin-1/2 antiferromagnetic Heisenberg model. In this talk, I will discuss recent optical second harmonic generation results on a model insulating cuprate Sr₂CuO₂Cl₂, which show evidence of anomalous broken symmetries suggesting physics beyond these simple models.