Size effects, phase slip, and the origin off−αnoise inNbSe3

The threshold electric field for charge-density-wave (CDW) depinning in ${\mathrm{NbSe}}_3$ varies inversely with crystal thickness. Since the thickness of nearly all ${\mathrm{NbSe}}_3$ crystals varies in steps across their width, a macroscopic inhomogeneity in CDW pinning results. We show that CDW phase slip occurring along thickness steps provides the dominant source of broadband noise in ${\mathrm{NbSe}}_3$, and is responsible for complicated narrow-band noise spectra and mode-locking behavior. In crystals with no thickness steps, the evidence for scaling behavior of the CDW current near threshold is not convincing.