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Creep motion of an intruder within a granular glass close to jamming

We investigate experimentally the dynamics of an intruder dragged by a constant force in an assembly of horizontally vibrated grains close to jamming. At moderate packing fractions, the intruder moves rapidly as soon as the force is applied. Above some threshold value of the packing fraction which increases with the applied force, the intruder exhibits an intermittent creep motion with strong fluctuations reminiscent of a crackling noise signal. These fluctuations behave in a critical manner at the jamming transition unveilled in a previous study. The transition separates a regime where the intruder motion is dominated by local free volume rearrangements from a regime where the instantaneous displacement field is strongly heterogeneous and resemble the force chains patterns observed in dense granular packings.