Dynamic metastable vortex states in interacting vortex lines

TL;DR

This paper investigates the complex dynamic behavior of vortices in superconducting nano-bridges, revealing metastable states and fractional Shapiro steps that could be harnessed for quantum device applications.

Contribution

It introduces the concept of metastable vortex states in nano-bridges with crossing defects and analyzes their dynamic locking behavior under RF excitation.

Findings

Metastable vortex states can be locked to RF drive.

Fractional Shapiro steps arise from anharmonic vortex motion.

Voltage jumps correspond to lock-unlock transitions.

Abstract

The electron transport in current-biased superconducting nano-bridges is determined by the motion of the quantum vortex confined in the internal disorder landscape. Here we consider a simple case of a single or two neighbouring linear defects crossing a nano-bridge. The strong anharmonicity of the vortex motion along the defect leads, upon RF-excitation, to fractional Shapiro steps. In the case of two defects, the vortex motion becomes correlated, characterized by metastable states that can be locked to a resonant RF-drive. The lock-unlock process causes sudden voltage jumps and drops in the voltage-current characteristics observed in experiments. We analyze the parameters promoting these metastable dynamic states and discuss their potential applications in quantum devices.