Optical studies of symmetry breaking in cuprate superconductors*

We probe the spectral character of broken symmetry states in high –temperature cuprate superconductors (HTS) using polarization sensitive Faraday rotation measurements. We measure the complex Faraday angleat zero magnetic field on a series of HTS thin films with various levels of doping as a function of energy (0.1-3 eV), temperature (10-300K) and sample orientation. We observe sinusoidal variation of Faraday rotation angle with respect to the sample orientation (linear dichroism) which indicates the presence of broken linear symmetry. The amplitude of the linear dichroism signal is strongest in the underdoped films and increases with decreasing temperature.