Three-Dimensional Phase-Kink State in Thick Stack of Josephson Junctions and Terahertz Radiation

TL;DR

This paper investigates the three-dimensional phase-kink state in thick stacks of Josephson junctions, revealing how geometry influences resonance frequencies and providing insights into the mechanism behind strong terahertz radiation.

Contribution

The study extends the phase-kink state to three dimensions in Josephson junction stacks and analyzes how geometry affects resonance frequencies and radiation mechanisms.

Findings

Cylindrical mesas have higher resonance frequencies than square ones of the same size.

Resonance frequency depends on the radius of cylindrical mesas, confirming the kink state.

The results help explain the mechanism of strong terahertz radiation observed experimentally.

Abstract

The dynamics of superconductivity phase in thick stack of Josephson junctions with strong inductive coupling, such as the one realized in layered high-$T_c$ cuprates and possibly the recently discovered FeAs-based superconductors, is investigated under a c-axis bias voltage and in the absence of an external magnetic field. The kink state found previously by the present authors is extended to three dimensions for both rectangular and cylindrical geometries. The IV characteristics are calculated and the distributions of electromagnetic field inside the samples are clarified. The solution for a cylindrical mesa exhibits a higher resonating frequency than that of a square mesa with the same linear size by a factor of $\sim 2.4$. More importantly, from the radius dependence of the resonance frequency for the cylinder geometry it is possible to confirm directly the kink state, and thus to reveal the mechanism of the strong radiation discovered in recent experiments.