title: Scale-free channeling patterns near the onset of erosion of sheared granular beds.
abstract: Erosion shapes our landscape and occurs when a sufficient shear stress is exerted by a fluid on a sedimented layer. What controls erosion at a microscopic level remains debated, especially near the threshold forcing where it stops. Here we study, experimentally, the collective dynamics of the moving particles, using a setup where the system spontaneously evolves toward the erosion onset. We find that the spatial organization of the erosion flux is heterogeneous in space and occurs along channels of local flux σ whose distribution displays scaling near threshold and follows [Formula: see text], where J is the mean erosion flux. Channels are strongly correlated in the direction of forcing but not in the transverse direction. We show that these results quantitatively agree with a model where the dynamics is governed by the competition of disorder (which channels mobile particles) and particle interactions (which reduces channeling). These observations support that, for laminar flows, erosion is a dynamical phase transition that shares similarity with the plastic depinning transition occurring in dirty superconductors. The methodology we introduce here could be applied to probe these systems as well.
authors.affiliation: Aix-Marseille Université, CNRS, Institut Universitaire des Systèmes Thermiques Industriels, 13453 Marseille, France.
authors.forename: Pascale
authors.initials: P
authors.lastname: Aussillous
authors.affiliation: Aix-Marseille Université, CNRS, Institut Universitaire des Systèmes Thermiques Industriels, 13453 Marseille, France.
authors.forename: Zhenhai
authors.initials: Z
authors.lastname: Zou
authors.affiliation: Aix-Marseille Université, CNRS, Institut Universitaire des Systèmes Thermiques Industriels, 13453 Marseille, France.
authors.forename: Élisabeth
authors.initials: É
authors.lastname: Guazzelli
authors.affiliation: Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106.
authors.forename: Le
authors.initials: L
authors.lastname: Yan
authors.affiliation: Institute of Physics, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland matthieu.wyart@epfl.ch.
authors.forename: Matthieu
authors.initials: M
authors.lastname: Wyart
keywords: dynamical phase transition; gravel bed river; plastic depinning