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

TL;DR

This paper introduces a modified RSJ model explaining subgap structures in the I-V characteristics of intrinsic Josephson junctions, linking them to phonon eigenfrequencies and suggesting a new measurement method for these phonons.

Contribution

It develops a modified RSJ model that couples Josephson oscillations with c-axis phonons, explaining subgap structures and proposing a novel phonon measurement technique.

Findings

Subgap structures align with longitudinal optical phonon frequencies.

Enhanced microwave emission observed at subgap voltages.

Model accurately explains experimental I-V characteristics.

Abstract

A modified RSJ-model for the coupling of intrinsic Josephson oscillations and c-axis phonons in the high-T_c superconductors Tl_2Ba_2Ca_2Cu_3O_{10+\delta} and Bi_2Sr_2CaCu_2O_{8+\delta} is deveoped. This provides a very good explanation for recently reported subgap structures in the I-V-characteristic 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.