Microwave-induced flow of vortices in long Josephson junctions

TL;DR

This study demonstrates that microwave radiation induces vortex flow in long Josephson junctions, altering their electrical characteristics in a manner similar to magnetic field effects, with irregular vortex motion explained by chaos and multi-photon absorption analogies.

Contribution

The paper provides the first combined experimental and numerical evidence of microwave-driven vortex flow in long Josephson junctions and introduces an analogy with incoherent multi-photon absorption and chaos control.

Findings

Microwave radiation induces vortex flow similar to flux-flow behavior.

Vortex motion becomes irregular and chaotic under microwave drive.

The $I$-$V$ characteristics depend on microwave power as $V_s \\propto P^{0.5}$.

Abstract

We report experimental and numerical study of microwave-induced flow of vortices in long Josephson junctions at zero dc magnetic field. Our intriguing observation is that applying an ac-bias of a small frequency $f \ll f_p $ and sufficiently large amplitude changes the current-voltage characteristics ($I$-$V$ curve) of the junction in a way similar to the effect of dc magnetic field, well known as the flux-flow behavior. The characteristic voltage $V$ of this low voltage branch increases with the power $P$ of microwave radiation as $V_{s}\propto P^{\alpha}$ with the index $\alpha \simeq 0.5 $. Experiments using a low-temperature laser scanning microscope unambiguously indicate the motion of Josephson vortices driven by microwaves. Numerical simulations agree with the experimental data and show strongly {\it irregular} vortex motion. We explain our results by exploiting an analogy between the microwave-induced vortex flow in long Josephson junctions and incoherent multi-photon absorption in small Josephson junctions in the presence of large thermal fluctuations. In the case of long Josephson junctions the spatially-temporal chaos in the vortex motion mimics the thermal fluctuations. In accordance with this analogy, a control of the intensity of chaos in a long junction by changing its damping constant leads to a pronounced change in the shape of the $I$-$V$ curve. Our results provide a possible explanation to previously measured but not yet understood microwave-driven properties of intrinsic Josephson junctions in high-temperature superconductors.