Cages and anomalous diffusion in vibrated dense granular media

Abstract

A vertically shaken granular medium hosts a blade rotating around a fixed vertical axis, which acts as a mesorheological probe. At high densities, independently from the shaking intensity, the blade's dynamics show strong caging effects, marked by transient sub-diffusion and a maximum in the velocity power density spectrum (vpds), at a resonant frequency $\sim 10$ Hz. Interpreting the data through a diffusing harmonic cage model allows us to retrieve the elastic constant of the granular medium and its collective diffusion coefficient. For high frequencies $f$, a tail $\sim 1/f$ in the vpds reveals non-trivial correlations in the intra-cage micro-dynamics. At very long times (larger than $10$ s), a super-diffusive behavior emerges, ballistic in the most extreme cases. Consistently, the distribution of slow velocity inversion times $\tau$ displays a power-law decay, likely due to persistent collective fluctuations of the host medium.

5 pages + 4 page of supplemental material, 6 figures, to be published on Phys. Rev. Lett

References in corpus (3)

• Caging dynamics in a granular fluid
• Critical scaling and heterogeneous superdiffusion across the jamming/rigidity transition of a granular glass
• Nonequilibrium Brownian motion beyond the effective temperature

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• Effective Equations in complex systems: from Langevin to machine learning