Depinning and anisotropic order in flowing and static vortex lattices inNbSe2studied with magnetic decoration

Vortex lattice dynamics is studied by magnetic decoration experiments on ${\mathrm{NbSe}}_{2}$ at fields of 20\char21{}70 G. At depinning the motion begins along the principal lattice directions which are nearest to the direction of the driving force. The periodicity in the direction transverse to the motion is preserved. Along the flow channels, however, large variations of the intervortex spacing are observed. When the vortex lattice comes to a stop, the static structure partially preserves the displacement characteristics of the moving lattice, as follows from the anisotropy of the angular dependence of the vortex displacement correlator.