Crossover in low-temperature collective spin-density-wave transport

Abstract

We have measured the nonlinear transport in the spin-density-wave (SDW) state of (TMTSF${)}_{2}$${\mathrm{PF}}_{6}$. Besides the typical sliding SDW conduction, at temperatures close to ${\mathit{T}}_{\mathrm{SDW}}$, we find a new type of collective electron transport below T\ensuremath{\simeq}1 K, with temperature-independent conductivity which follows a Zener-type expression. We discuss the relevant energy scales of the ground-state excitations, both for single-particle tunneling and for coherent SDW processes.