Breathing Charge Density Waves in Intrinsic Josephson Junctions

TL;DR

This paper demonstrates the formation of breathing charge density waves in layered superconductors with Josephson junctions, revealing complex dynamics under electromagnetic irradiation and new features in Shapiro step behavior.

Contribution

It introduces the concept of breathing charge density waves in coupled Josephson junctions and analyzes their transformation, transitions, and electromagnetic response.

Findings

Charge density waves form along coupled Josephson junction stacks.

Transitions between different CDW types are demonstrated.

Shapiro steps do not directly match radiation frequency, indicating collective behavior.

Abstract

We demonstrate the creation of a charge density wave (CDW) along a stack of coupled Josephson junctions in layered superconductors. Electric charge in each superconducting layer oscillates around some average value, forming a breathing CDW. We show the transformation of a longitudinal plasma wave to CDW in the state corresponding to the outermost branch. Transitions between different types of CDW's related to the inner branches of current voltage characteristics are demonstrated. The effect of the external electromagnetic irradiation on the states corresponding to the inner branches differs crucially from the case of the single Josephson junction. The Shapiro steps in the IV-characteristics of the junctions in the stack do not correspond directly to the frequency of radiation $\omega$. The system of Josephson junctions behaves like a single whole system: the Shapiro steps or their harmonics in the total IV-characteristics appear at voltage $\sum V_l=N_R\frac{m}{n}\omega$, where $V_l$ is the voltage in $l$-th junction, $N_R$ is the number of JJ in the rotating state, and $m$ and $n$ are integer numbers.