Vortex-Array Model for Charge-Density-Wave Conduction Noise

It is proposed that ac voltage ($v_{\mathrm{a}\mathrm{}\mathrm{c}}$) oscillations observed in sliding charge-density-wave systems are caused by phase vortices at the sample ends. The model's prediction that $v_{\mathrm{a}\mathrm{}\mathrm{c}}$ is length independent is verified experimentally. The long-range phase coherence implied by thermal-gradient experiments is consistent with the vortex model but not with models based on impurities.