Abstract
Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order
rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex
lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in
MgB2 as it was driven from a metastable to the ground state through a series of small changes in the
applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of
substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning.
Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a
rotation to the ground state orientation.
