Josephson Plasma in Various High-T c Cuprates

Josephson plasma in various high-T_ccuprates with and without magnetic field is studied by using the sphere resonance method. For Bi₂Sr₂CaCu₂O₈₊, the plasma in a zero magnetic field exists at 5 cm^–1for a slightly overdoped sample (T_c= 85 K) and shifts to 11 cm^–1as the doping increases (T_c= 71 K). For SmLa_1–xSr_xCuO_3.95(T* phase), two peaks appear at 11 and 30 cm^–1in a zero magnetic field, and both peaks shift to lower frequencies as the magnetic field increases. These peaks are identified as the Josephson plasma of the intrinsic Josephson junction at the fluorite-type Sm₂O₂block layer and the rocksalt-type (La,Sr)₂O_2–block layer, respectively. This indicates that the T* phase can be regarded as the ···S/I/S/I/S/I/S/I/S··· (···superconductor/insulator1/superconductor/insulator2/superconductor···) -type Josephson junction array.