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

Abstract

The ab-plane dielectric function at 3392nm of thin films of YBa 2Cu 3O 7−δ with a wide range of doping has been measured using attenuated total reflectance. While ε 2, and therefore σ 1, are temperature independent, | ε 1| decreases by ∼25% with increasing temperature. A stronger dependence on doping is observed: the magnitudes of ε 1 and ε 2 are both strongly suppressed as δ increases. A generalised Drude analysis shows that the plasma frequency is temperature-independent, but scales with doping. The scattering rate increases with temperature, and also increases with decreasing doping, consistent with stronger coupling in the underdoped regime.