Depinning of disordered bosonic chains

TL;DR

This paper investigates the depinning transition of one-dimensional disordered bosonic chains, relevant for superconducting systems, revealing how chain length and disorder influence the onset of transport.

Contribution

It provides a numerical analysis of depinning in short and weakly disordered bosonic chains, highlighting the role of the Larkin length and emergent correlation scales.

Findings

Depinning voltage saturates for chains shorter than the Larkin length.

Weak disorder introduces a correlation length affecting transport onset.

Transport in short arrays is dominated by soliton penetration.

Abstract

We consider one-dimensional bosonic chains with a repulsive boson-boson interaction that decays exponentially on large length-scales. This model describes transport of Cooper-pairs in a Josepshon junction array, or transport of magnetic flux quanta in quantum-phase-slip ladders, i.e. arrays of superconducting wires in a ladder-configuration that allow for the coherent tunnelling of flux quanta. In the low-frequency, long wave-length regime these chains can be mapped to an effective model of a one-dimensional elastic field in a disordered potential. The onset of transport in these systems, when biased by external voltage, is described by the standard depinning theory of elastic media in disordered pinning potentials. We numerically study the regimes that are of relevance for quantum-phase-slip ladders. These are (i) very short chains and (ii) the regime of weak disorder. For chains shorter than the typical pinning length, i.e., the Larkin length, the chains reach a saturation regime where the depinning voltage does not depend on the decay length of the repulsive interaction. In the regime of weak disorder we find an emergent correlation length-scale that depends on the disorder strength. For arrays shorter than this length the onset of transport is similar to the clean arrays, i.e., is due to the penetration of solitons into the array. We discuss the depinning scenarios for longer arrays in this regime.