Far-infrared ab plane reflectance and transmission of Bi2Sr2CaCu2O8

We review recent experimental data on the infrared thin film transmission and single crystal reflection spectra of Bi2Sr2CaCu2O8 (Tc ∼ 85 K). Both show that the low frequency response can be described by a Drude absorption with a relaxation rate for the carriers of the order of 100 cm−1. This places the materials in the clean limit and no superconducting gap structure is evident. A temperature independent midinfrared absorption is present with a sharp onset at 300 cm−1.