COUPLING BETWEEN PHONONS AND INTRINSIC JOSEPHSON OSCILLATIONS IN CUPRATE SUPERCONDUCTORS

The recently reported subgap structures in the current-voltage charact eristic of intrinsic Josephson junctions in the high-T-c superconducto rs Tl2Ba2Ca2Cu3O10+delta and Bi2Sr2CaCU2O8+delta are explained by the coupling between c-axis phonons and Josephson oscillations. A model is developed where c-axis lattice vibrations between adjacent supercondu cting multilayers are excited by the Josephson oscillations in a resis tive junction. The voltages of the lowest structures correspond well t o the frequencies of longitudinal c-axis phonons with large oscillator strength in the two materials, providing a new measurement technique for this quantity.