Motional ordering of a charge-density wave in the sliding state

We have used high-resolution x-ray scattering, in the presence of an applied direct current, for studying the correlation lengths in the sliding charge-density wave (CDW) state. Transport properties were simultaneously measured in situ during the experiment. We find that, while the transverse correlation is reduced when the CDW moves, the CDW becomes more ordered in the direction of motion. This is the first report of a motional ordering process in a periodic system other than a vortex lattice.