Theory for the coupling between longitudinal phonons and intrinsic Josephson oscillations in layered superconductors

TL;DR

This paper develops a microscopic theory describing how intrinsic Josephson oscillations in layered superconductors couple with longitudinal phonons, explaining subgap structures in I-V characteristics through phonon resonances.

Contribution

It introduces a comprehensive model linking Josephson oscillations with lattice vibrations, explaining experimental subgap features in cuprate superconductors.

Findings

Resonances occur at van Hove singularities of phonon branches.

Lattice vibrations influence c-axis transport via an effective dielectric function.

Phonon dispersion affects resonance damping and inter-junction coupling.

Abstract

In this publication a microscopic theory for the coupling of intrinsic Josephson oscillations in layered superconductors with longitudinal c-axis-phonons is developed. It is shown that the influence of lattice vibrations on the c-axis transport can be fully described by introducing an effective longitudinal dielectric function. Resonances in the I-V-characteristic appear at van Hove singularities of both acoustical and optical longitudinal phonon branches. This provides a natural explanation of the recently discovered subgap structures in the I-V-characteristic of highly anisotropic cuprate superconductors. The effect of the phonon dispersion on the damping of these resonances and the coupling of Josephson oscillations in different resistive junctions due to phonons are discussed in detail.