DYNAMICAL CONDUCTIVITY OF HIGH-TC SUPERCONDUCTORS

We present an analysis of the far- and mid-infrared conductivity of YBa2Cu3O7-y. We suppose that two types of low-lying electronic excitations in high-Tc superconductors are present, namely mobile quasi holes in the CuO2 planes and almost localized doping electron states in the CuO3 chains. We explain the far-infrared conductivity at low temperature (T ≪ Tc) with a two-band model derived from the two-layer structure of YBa2Cu3O7-y. This model leads to two gap values, well above and below the BCS value. © 1990.