Coupling between phonons and intrinsic Josephson oscillations in cuprate superconductors

TL;DR

This paper explains subgap structures in high-T_c superconductor Josephson junctions as resulting from coupling between c-axis phonons and Josephson oscillations, offering a new way to measure phonon properties.

Contribution

It introduces a model linking c-axis phonons and Josephson oscillations, explaining experimental subgap features in cuprate superconductors.

Findings

Subgap structures align with longitudinal c-axis phonon frequencies.

The model provides a new measurement method for phonon oscillator strength.

Experimental data supports the phonon-Josephson coupling explanation.

Abstract

The recently reported subgap structures observed in the current-voltage characteristic of intrinsic Josephson junctions in the high-T_c superconductors Tl_2Ba_2Ca_2Cu_3O_{10+\delta} and Bi_2Sr_2CaCu_2O_{8+\delta} are explained by the coupling between c-axis phonons and Josephson oscillations. A model is developed where c-axis lattice vibrations between adjacent superconducting multilayers are excited by the Josephson oscillations in a resistive junction. The voltages of the lowest structures correspond well to the frequencies of longitudinal c-axis phonons with large oscillator strength in the two materials, providing a new measurement technique for this quantity.