  We study shear-driven jamming of ellipsoidal particles at zero temperature
with a focus on the microscopic dynamics. We find that a change from spherical
particles to ellipsoids with aspect ratio $\alpha=1.02$ gives dramatic changes
of the microscopic dynamics with much lower translational velocities and a new
role for the rotations. Whereas the velocity difference at contacts---and
thereby the dissipation---in collections of spheres is dominated by the
translational velocities and reduced by the rotations, the same quantity is in
collections of ellipsoids instead totally dominated by the rotational
velocities. By also examining the effect of different aspect ratios we find
that the examined quantities show either a peak or a change in slope at
$\alpha\approx1.2$, thus giving evidence for a crossover between different
regions of low and high aspect ratio.

Soft Condensed Matter