Observation of the transverse optical plasmon in SmLa0.8Sr0.2CuO4-delta

We present microwave and infrared measurements on SmLa0.8Sr0.2CuO4-delta, w hich are direct evidence for the existence of a transverse optical plasma m ode, observed as a peak in the c-axis optical conductivity. This mode appea rs as a consequence of the existence of two different intrinsic Josephson c ouplings between the CuO2 layers, one with a Sm2O2 block layer, and the oth er one with a (La, Sr)(2)O2-delta block layer. From the frequencies and the intensities of the collective modes we determine the value of the compress ibility of the two dimensional electron fluid in the copper oxygen planes.