Observation of correlations up to the micrometer scale in sliding charge-density waves

A high resolution coherent x-ray diffraction experiment has been performed on the charge-density wave (CDW) system K0.3MoO3. The 2k(F) satellite reflection associated with the CDW has been measured with respect to external dc currents. In the sliding regime, the 2k(F) satellite reflection displays secondary satellites along the chain axis which corresponds to correlations up to the micrometer scale. This super long-range order is 1500 times larger than the CDW period itself. This new type of electronic correlation seems inherent to the collective dynamics of electrons in charge-density wave systems. Several scenarios are discussed.