Experimental evidences of the Gardner phase in a granular glass

TL;DR

This study provides experimental evidence of a Gardner phase in a vibrated granular glass, showing that particles explore different configurations under repeated compression while the local structure remains stable.

Contribution

It offers the first experimental demonstration of the Gardner phase in a granular glass, aligning experimental results with recent numerical and theoretical predictions.

Findings

Particles select different vibrational positions across cycles

Mean square displacement aligns with cage separation measurements

Distribution of cage order parameters shows heterogeneities

Abstract

Analyzing the dynamics of a vibrated bi-dimensional packing of bidisperse granular discs below jamming, we provide evidences of a Gardner phase deep into the glass phase. To do so we perform several independent compression cycles within the same glass and show that the particles select different average vibrational positions at each cycle, while the neighborhood structure remains unchanged. We compute the mean square displacement as a function of the packing fraction and compare it with the average separation between the cages obtained for different compression cycles. Our results are fully compatible with recent numerical observations obtained for a mean field model of glass as well as for hard spheres in finite dimension. We also characterize the distribution of the cage order parameters. Here we note several differences from the numerical results, which could be attributed to activated processes and cage heterogeneities.