Avalanche Criticality Drives the Physical Aging of Disordered Matter:
from Crumpled Sheets to Seismic Aftershocks
Monday November 18th at 14:00
Wolfson Building of Mechanical Engineering, Room 206
Abstract:
Many complex and disordered systems fail to reach equilibrium after they have been quenched or perturbed. Instead, they sluggishly relax toward equilibrium at an ever-slowing, history dependent rate, a process termed physical aging. The microscopic processes underlying the dynamic slowdown during aging and the reason for its similar occurrence in different systems remain poorly understood.
Combining experiments on crumpled sheets and simulations of a disordered network of interacting elastic instabilities, we reveal the structural mechanism underlying logarithmic aging in these systems. We find that under constant external loading, the system self-organizes to a marginally stable state, where it can remain for long, but finite, times. The system’s slow relaxation is intermittent, and advances via self-similar, slow avalanches of localized, micro-mechanical instabilities.
These avalanches are thermal – they span many timescales and are driven by facilitation and noise. The avalanches’ size and the inter-instability times are power-law distributed and exhibit a unique property – the distributions maintain their scaling exponents throughout the ageing process, but their cut-offs grow in time. Crucially, the quiescent dwell times between avalanches grow in proportion to the system’s age, which leads to the observed dynamic slow-down and logarithmic aging. We link this effect to a slow increase of the lowest local energy barriers, which we find govern the initiation of avalanches.
Applying our analysis to the temporal dynamics of seismic aftershocks reveals strikingly similar results, suggesting that a similar physical mechanism underlies aftershock dynamics and the celebrated phenomenology of Omori’s law.
:Bio
Yoav Lahini earned a B.Sc. in physics from the Hebrew University, and an M.Sc. and PhD in Physics from the Weizmann Institute, working on nonlinear and quantum optics in disordered media. He then spent three years at MIT as a Pappalardo postdoctoral fellow and two additional years at Harvard as a research associate, working on the far-from-equilibrium dynamics of complex and disordered systems. In 2017 Yoav opened the Soft and Complex Matter Lab in the school of Physics at Tel Aviv university.
