Anisotropic finite-size scaling of an elastic string at the depinning threshold in a random-periodic medium

TL;DR

This study investigates how the geometry of a driven elastic string at its depinning threshold in random-periodic media scales anisotropically, revealing a crossover behavior influenced by the ratio of transverse periodicity to longitudinal size.

Contribution

It introduces a detailed numerical analysis of the anisotropic finite-size scaling of an elastic string at depinning, highlighting the role of the ratio between transverse and longitudinal sizes in controlling roughness properties.

Findings

The average square width exhibits a non-trivial minimum at a specific ratio k.

Crossover from random-periodic to random-manifold roughness occurs around k ~ 1.

Large k behavior shows anomalous roughness and subleading corrections.

Abstract

We numerically study the geometry of a driven elastic string at its sample-dependent depinning threshold in random-periodic media. We find that the anisotropic finite-size scaling of the average square width $\bar{w^2}$ and of its associated probability distribution are both controlled by the ratio $k=M/L^{\zeta_{\mathrm{dep}}}$, where $\zeta_{\mathrm{dep}}$ is the random-manifold depinning roughness exponent, $L$ is the longitudinal size of the string and $M$ the transverse periodicity of the random medium. The rescaled average square width $\bar{w^2}/L^{2\zeta_{\mathrm{dep}}}$ displays a non-trivial single minimum for a finite value of $k$. We show that the initial decrease for small $k$ reflects the crossover at $k \sim 1$ from the random-periodic to the random-manifold roughness. The increase for very large $k$ implies that the increasingly rare critical configurations, accompanying the crossover to Gumbel critical-force statistics, display anomalous roughness properties: a transverse-periodicity scaling in spite that $\bar{w^2} \ll M$, and subleading corrections to the standard random-manifold longitudinal-size scaling. Our results are relevant to understanding the dimensional crossover from interface to particle depinning.