c-axis excitations in high-T-c superconductors detected by grazing incidence reflectivity measurements

Measuring absolute reflectivity at an angle of incidence of 80 degrees for Tl2Ba2CuO6, Bi2Sr2CuO6, Nd(1.85)Ce(0.15)CuO4 with p-polarized light (plane of incidence normal to the CuO2-planes), we were able to extract the c-axis longitudinal optical modes in the normal and superconducting state. Superconducting induced changes in the electronic c-axis properties will be discussed and compared to La2-xSrxCuO4 and YBa2Cu3Oy where a superfluid plasma edge is observed at low frequencies.