Dissociation Transition of a Composite Lattice of Magnetic Vortices in the Flux-Flow Regime of Two-Band Superconductors

TL;DR

This paper predicts a dissociation transition of composite vortices in two-band superconductors under flux-flow conditions, leading to increased resistivity and observable Shapiro steps, revealing complex vortex dynamics.

Contribution

It introduces the concept of vortex lattice dissociation in flux flow, highlighting the impact of current on vortex behavior in multiband superconductors.

Findings

Dissociation occurs at high currents, causing vortices to move independently.

Flux flow resistivity increases during dissociation.

Shapiro steps emerge in the dissociated phase with combined ac and dc currents.

Abstract

In multiband superconductors, each superconducting condensate supports vortices with fractional quantum flux. In the ground state, vortices in different bands are spatially bounded together to form a composite vortex, carrying one quantum flux \Phi_0. Here we predict dissociation of the composite vortices lattice in the flux flow state due to the disparity of the vortex viscosity and flux of the vortex in different bands. For a small driving current, composite vortices start to deform, but the constituting vortices in different bands move with the same velocity. For a large current, composite vortices dissociate and vortices in different bands move with different velocities. The dissociation transition shows up as an increase of flux flow resistivity. In the dissociated phase, Shapiro steps are developed when an ac current is superimposed with a dc current.