Vortex jamming in superconductors and granular rheology

TL;DR

This paper reveals a zero-temperature jamming transition in anisotropic Josephson junction arrays that parallels granular rheology, showing universal scaling and a fragile vortex state with directional superconducting and normal conducting behaviors.

Contribution

It demonstrates a novel zero-temperature jamming transition in JJAs and links it to granular rheology, introducing a new paradigm connecting superconductivity and soft material rheology.

Findings

Universal scaling in current-voltage curves near jamming

Anisotropic JJA exhibits directional vortex glass and liquid states

A theoretical model reproduces granular flow master curves

Abstract

We demonstrate that a highly frustrated anisotropic Josephson junction array(JJA) on a square lattice exhibits a zero-temperature jamming transition, which shares much in common with those in granular systems. Anisotropy of the Josephson couplings along the horizontal and vertical directions plays roles similar to normal load or density in granular systems. We studied numerically static and dynamic response of the system against shear, i. e. injection of external electric current at zero temperature. Current-voltage curves at various strength of the anisotropy exhibit universal scaling features around the jamming point much as do the flow curves in granular rheology, shear-stress vs shear-rate. It turns out that at zero temperature the jamming transition occurs right at the isotropic coupling and anisotropic JJA behaves as an exotic fragile vortex matter : it behaves as superconductor (vortex glass) into one direction while normal conductor (vortex liquid) into the other direction even at zero temperature. Furthermore we find a variant of the theoretical model for the anisotropic JJA quantitatively reproduces universal master flow-curves of the granular systems. Our results suggest an unexpected common paradigm stretching over seemingly unrelated fields - the rheology of soft materials and superconductivity.