Time-resolved stroboscopic neutron scattering of vortex lattice dynamics in superconducting niobium

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 direct microscopic measurements of the vortex lattice tilt modulus c(44) in ultrapure niobium using time-resolved small-angle neutron scattering. Aside from a general trend to faster vortex lattice dynamics for increasing temperatures, we observe a dramatic changeover of the relaxation process associated with the nontrivial 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.