Infrared symmetry breaking in YBa2Cu3O7-x as a function of energy, doping, and temperature

We explore the symmetry-breaking in cuprate high temperature superconductors (HTS) as a function of energy (117-2330 meV), doping, and temperature (30-300 K). We measure the Faraday rotation angle θ
_F
of transmitted radiation through thin YBa
₂
Cu
₃
O
_7-x
(YBCO) films as the sample is rotated. We observe twofold rotational symmetry in θ
_F
, which is associated with linear dichroism (LD) that can be generally associated with symmetry breaking. The LD signal shows a peak in the few hundred meV range and is strongest in under-doped films.