Subgap structures in the current-voltage characteristics of the intrinsic Josephson effect due to phonons

A modified RSJ model for the coupling of intrinsic Josephson oscillations and c-axis phonons in the high-T-c superconductors Tl2Ba2Ca2Cu3O10+delta and Bi2Sr2CaCu2O8+delta is developed. This provides a very good explanation for recently reported subgap structures in the I-V characteristics of the c-axis transport It turns out that the voltages of these structures coincide with the eigenfrequencies of longitudinal optical phonons, providing a new measurement technique for this quantity. The significantly enhanced microwave emission at the subgap structures in both the GHz and THz region is discussed. (C) 1997 Elsevier Science B.V.