Calculations of optical properties of high-temperature superconductors

The optical dielectric functions of the high- T c superconductors, Ba 0.6 K 0.4 BiO 3 , YBa 2 Cu 3 O 7 and Tl 2 Ba 2 Ca 2 Cu 3 O 10 , have been calculated using a tight-binding model. The results are compared to experimental data. The peak recently observed by De and Woollam at about 3.5 eV in the 2223 material is interpreted as O(2p) to Tl(6p) excitations.