Low-temperature divergence of the charge-density-wave viscosity in K0.30MoO3, (TaSe4)2I, and TaS3.

Abstract

We have measured the temperature dependence of the low-field, linear conductivity and the high-field, nonlinear conductivity resulting from charge-density-wave (CDW) motion in ${\mathrm{K}}_{0.30}$${\mathrm{MoO}}_{3}$, ${\mathrm{TaS}}_{3}$, and (${\mathrm{TaSe}}_{4}$${)}_{2}$I at zero frequency. In ${\mathrm{K}}_{0.30}$${\mathrm{MoO}}_{3}$ and (${\mathrm{TaSe}}_{4}$${)}_{2}$I, the nonlinear conductivity has a thermally activated behavior over an extended temperature range with activation energies which are nearly equal to that of the linear portion of the conductivity. In ${\mathrm{TaS}}_{3}$ the analysis is more complicated due to a large maximum in the threshold field, perhaps resulting from a commensurate-incommensurate transition, near 75 K. In ${\mathrm{TaS}}_{3}$, the nonlinear fraction of the conductivity has the same temperature dependence as the linear portion over a limited temperature range. In all materials the nonlinear conductivity vanishes at low temperatures. The charge carried by the CDW, measured by the current dependence of the ``washboard frequency,'' is relatively constant as function of temperature. These results indicate that viscous forces resulting from low-frequency damping of the CDW motion diverge as the temperature is lowered. We have also calculated the temperature dependence of the CDW relaxation time and static dielectric constant using experimental parameters. The excellent agreement attained gives strong support to a classical description of CDW transport in these materials.