Evidence for Tunneling of Charge-Density Waves in TaS3

The charge-density-wave contribution to ac and dc conductivity, rectification, and harmonic mixing has been measured on a single crystal of orthorhombic Ta${\mathrm{S}}_3$. A modified tunneling theory based on the Zener model of charge-density-wave conduction provides a detailed and quantitative account of these experiments. This evidence strongly supports the hypothesis that macroscopic quantum effects are observed in the megahertz frequency region at temperatures as high as 200 K.