  Superconducting vortex lattices, glasses and liquids attract great interest
as model systems of crystallization and as a source of microscopic information
of the nature of superconductivity. We report for the first time direct
microscopic measurements of the vortex lattice tilt modulus c44 in ultra-pure
niobium using time-resolved small angle neutron scattering. Besides a general
trend to faster vortex lattice dynamics for increasing temperatures we observe
a dramatic changeover of the relaxation process associated with the non-trivial
vortex lattice morphology in the intermediate mixed state. This changeover is
attributed to a Landau-branching of the Shubnikov domains at the surface of the
sample. Our study represents a showcase for how to access directly vortex
lattice melting and the formation of vortex matter states for other systems.
