OPTICAL ANISOTROPY AND ELECTRON PHONON COUPLING IN BI2SR2CACU2O8 SINGLE-CRYSTALS

We have determined the polarized reflectance spectra R parallel-to a, R parallel-to b and R parallel-to c of the high temperature superconductor Bi2Sr2CaCu2O8 in the normal state. The photon energy was varied between 30 meV and 6 eV. By fitting a Lorentz-Drude model or by performing a Kramers-Kronig analysis, respectively, the spectral distribution of the tensor components of the real and the imaginary part of the dielectric function were obtained. The optical results reveal a low electrical anisotropy within the (001) plane and a very high anisotropy between the in-plane conductivity and the conductivity perpendicular to this plane. The results confirm that Bi2Sr2CaCu2O8 is a 2D conductor. The spectrum R parallel-to c gives evidence for the interaction between infrared-active phonons and the low-energy part of interband transitions. From a quantitive fit, based on a Fano-resonance model, a strong electron-phonon coupling is deduced.