Damping of the spin-density-wave phase mode by defect scattering

Abstract

We have investigated the pinning of the spin-density wave and the low-frequency damping of the phase excitations in the solid solutions (TMTSF${)}_{2}$(${\mathrm{AsF}}_{6}$${)}_{1\mathrm{\ensuremath{-}}\mathit{x}}$(${\mathrm{SbF}}_{6}$${)}_{\mathit{x}}$ (0\ensuremath{\le}x\ensuremath{\le}1). The pinning is strongly enhanced by the weak nonmagnetic disorder introduced by the alloying. The damping is characterized by the nonlinear dc conductivity and by the dielectric relaxation. In a broad but limited temperature range we describe a temperature-independent damping with a strong dependence on defect concentration, suggesting elastic scattering of phasons by defects.