PHASE COHERENCE AND JOSEPHSON PLASMA IN BI2SR2CACU2O8+DELTA

The recently discovered Josephson plasma phenomena in layered high-T-c superconductors have opened possibilities for testing fundamental ide as of physics of high-T-c superconductivity as well as for the device applications at high frequencies above 100 GHz, The observation of Jos ephson plasma resonance manifests the existence of a series stack of e quivalent weak Josephson junctions between CuO2 layers in Bi2Sr2CaCu2O 8+delta, through which a Cooper pair can tunnel with phase coherence. This unique situation brings the superconducting plasma frequency into a microwave frequency region, simply because the number of Cooper pai rs participating in plasma phenomena is greatly reduced by the restric ted tunneling probability of Cooper pairs, It is known that two collec tive excitation modes, longitudinal and transverse modes, can exist in this case, Using a different dispersion relation between two modes we were able to separate two modes experimentally for the first time. Si nce the plasma resonance is the consequence of phase coherence between superconducting layers, the dynamical nature of the vortex state can in principle be studied by this technique. The results of the vortex c orrelation observed by the Josephson plasma resonance with and without correlated disorder is discussed. (C) 1997 Elsevier Science B.V.