Optical anisotropy of a cuprate high Tc superconductor

Evidence for a symmetry breaking phase transition across the pseudogap temperature T* of cuprate high-Tc superconductors has been reported in several experiments. For example, resonant ultrasound spectroscopy reveals a discontinuous change in the normal mode frequencies of the lattice across T* while spin-flip neutron scattering shows time reversal symmetry breaking across T*. Recent THz spectroscopy measurements also suggest the loss of mirror symmetries in the vicinity of T*. Optical anisotropy is in principle sensitive to the point group symmetries of a crystal and is highly complementary to the aforementioned techniques. I will present our progress in measuring and understanding the optical anisotropy of YBa$_{2}$Cu$_{3}$O$_{y}$ in the vicinity of its pseudogap transition temperature.