Optical conductivity in the superconducting state of layered cuprate oxides

The optical conductivity for very low frequencies is investigated in the superconducting state of YBa2Cu3O7 using a layered structure model that some pairing interaction generates superconductivity in the CuO2-plane layers and the interlayer transfer interaction induces weak superconductivity in the Cu-O chain layers. The optical conductivity has contributions from the plane and chain layers which show a striking difference in the temperature dependence below Tc. The optical conductivity of the plane layers has a peak just below Tc, which is similar to the Hebel-Slichter peak in the nuclear relaxation rate, and decreases rapidly below the temperature of the peak, while the optical conductivity of the chain lauers monotonically increases with decreasing temperature. The temperature dependence of the optical conductivity is compared with that of the nuclear relaxation rate. (orig.)