CHARGE DYNAMICS ACROSS THE CUO2 PLANES IN LA2-XSRXCUO4

Infrared reflectivity measurements on high-quality single crystals of La2-xSrxCuO4 were performed with polarization perpendicular to the CuO2 planes (E parallel-to c). The c-axis spectrum shows a dramatic change at T(c), from a featureless spectrum above T(c) to the one with a sharp reflectivity edge below T(c). We find that the spectrum below T(c) is dominated by the plasma edge arising from the carriers condensed in the superconducting state, not by a superconducting gap excitation, and that the superconducting transition is accompanied by the onset of coherent charge transport along the c axis.