Dielectric function of YBCO in the mid-infrared: temperature and doping dependence at 3.392 mu m

The ab-plane dielectric function at 3392mm of thin films of YBa2Cu3O7-delta with a wide range of doping has been measured using attenuated total refle ctance. while epsilon (2), and therefore sigma (1), are temperature indepen dent, /epsilon (1)/ decreases by similar to 25% with increasing temperature . A stronger dependence an doping is observed: the magnitudes of epsilon (1 ) and epsilon (2) are both strongly suppressed as delta increases. A genera lised Drude analysis shows that the plasma frequency is temperature-indepen dent, but scales with doping. The scattering rate increases with temperatur e, and also increases with decreasing doping, consistent with stronger coup ling in the underdoped regime.