Double Josephson plasma in SmLa1-xSrxCuO4-delta

Josephson plasma in T* phase SmLa1-xSrxCuO4-delta is studied by the sphere resonance method for powder samples and by the reflectivity measurement of single crystals. In the sphere resonance method, two peaks appear below Tc. Both peaks shift to higher frequencies as the doping increases and are obs erved at 12 and 30 cm(-1) for SmLa0.85Sr0.15CuO3.985 (T-c = 31 K). The osci llator strength of the peak at the higher frequency is much smaller than th at at the lower frequency. The same changes are also observed in the reflec tivity measurement along the c-axis; two reflectivity edges are observed be low T-c, the edges shift to higher frequencies as the doping increases, and the edge at higher frequency is smaller than that at lower frequency. Thes e observations confirm that the system can be regarded as the... supercondu ctor/insulatorl/superconductor/insulator2/superconductor...- type Josephson junction array. The reason for the smallness of the plasma at higher frequ ency, which is inconsistent with the prediction of the multilayer model, is also discussed. (C) 2001 Elsevier Science B.V. All rights reserved.