Experimental test of the interlayer pairing models for high-T-c superconductivity using grazing-incidence infrared reflectometry

From measurements of the far-infrared reflectivity at grazing angles of incidence with p-polarized light we determined the c-axis Josephson plasma frequencies of the single layer high-T-c cuprates Tl2Ba2CuO6 and La2-xSrxCuO4. We detected a strong plasma resonance at 50 cm(-1) for La2-xSrxCuO4 in excellent agreement with previously published results. For Tl2Ba2CuO6 we were able to determine an upper limit of the unscreened c-axis Josephson plasma frequency 100 cm(-1) or a c-axis penetration depth >15 mu m. The small value of omega(J) stands in contrast to recent a prediction based on the interlayer tunneling mechanism of superconductivity.