Anisotropy and field-dependence of the spin-density-wave dynamics in the quasi one-dimensional conductor (TMTSF)<Subscript>2</Subscript>PF<Subscript>6</Subscript>

The anisotropic and non-linear transport properties of the quasi one-dimensional organic conductor (TMTSF)<Subscript>2</Subscript>PF<Subscript>6</Subscript> have been studied by dc, radiofrequency, and microwave methods. Microwave experiments along all three axes reveal that collective transport, which is considered to be the fingerprint of the spin-density-wave condensate, also occurs in the perpendicular b<Superscript>′</Superscript> direction. The pinned mode resonance is present in the a and b<Superscript>′</Superscript>-axes response, but not along the least conducting c<Superscript>*</Superscript> direction. The ac-field threshold, above which the spin-density-wave response is non-linear, strongly decreases as the temperature drops below 4 K. With increasing strength of the microwave electric field and of the radiofrequency signal, the pinned mode and the screened phason loss-peak shift to lower frequencies. In the non-linear regime, in addition to the phason relaxation mode with Arrhenius-like resistive decay, an additional mode with very long and temperature-independent relaxation time appears below 4 K. We attribute the new process to short-wavelength excitations associated with discommensurations of the spin density wave close to commensurability. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005