Conduction noise in sliding charge-density waves

Abstract

The conduction noise from sliding charge-density waves (CDWs) is studied in NbSe$\sb3$ and K$\sb{0.3}$MoO$\sb3$ (blue bronze). A statistical analysis of the fluctuations in the noise is presented: the probability distributions of the fluctuating spectral components, the power spectra of these fluctuations (i.e. the second spectra), and their correlation functions all indicate that the ac signal accompanying CDW conduction is Gaussian noise. An important consequence of the Gaussian statistics is that the size of the conduction noise is completely characterized by the second moment of its distribution, the rms voltage. This property is instrumental in making reliable measurements of the conduction noise size.

Exploiting this reliability, further experiments characterize the behavior of the conduction noise rms voltage as a function of electrical bias and temperature (in both materials), and specimen length (in blue bronze). The principal results of these investigations are: the size of the noise as a function of conduction noise frequency $f\sb{0}$ increases and then saturates; saturation occurs when $f\sb{0}$ exceeds the material's dielectric relaxation frequency; and the size of the noise in blue bronze increases linearly with specimen length.

The principal conclusions of this work are: randomness is central to CDW dynamics; the rms voltage is a reliable and precise characterization of the size of the conduction noise; dielectric relaxation is an important limiting process in CDW sliding; the conduction noise is generated throughout the entire volume of the blue bronze crystals and is intrinsic to CDW conduction; and the length of temporally phase-coherent domains in blue bronze (at 77K) is as long as the specimens themselves.