Revealing 3D granular glassy dynamics with Magnetic Resonance Particle Tracking

When externally driven granular matter is increasingly compressed, it undergoes a slowdown of particle dynamics, eventually freezing into a disordered jammed state. Here, we make use of Magnetic Resonance Particle Tracking (MRPT) [1], a versatile new technique that permits tracking many particles simultaneously, with resolution on the scale of micrometers and milliseconds, while preserving their identity. We show that MRPT enables the direct study of granular glassy dynamics in 3D for both monodisperse and polydisperse particles. We vary the volume fraction of a confined vibrated granular system and investigate it over 5 temporal orders of magnitude down to the ballistic regime, studying the effect of confinement and polydispersity. Resulting particle trajectories indicate collective behavior in the form of caging dynamics typical of thermal glass-forming systems. In particular, tracking multiple particles with identity preservation allows for the study of higher-order correlations as reflected by the van Hove function, which provide information about structure and structural memory. A two-step relaxation process is seen in the plateauing of the mean-squared displacement of particles and the intermediate scattering function. Moreover, the probability density function of particle displacements exhibits exponential tails indicative of spatially heterogeneous dynamics.

[1] M. Suter, J. P. Metzger, A. Port, C. R. Müller, and K. P. Pruessmann, (2025), p. arXiv:2503.22425.