Bimodal Energy Relaxation in Quasi-One-Dimensional Compounds with a Commensurate Modulated Ground State

Abstract

We show that the low temperature ($T<0.5\text{ }\text{ }\mathrm{K}$) time dependent nonexponential energy relaxation of quasi-one-dimensional compounds strongly differs according to the nature of their modulated ground state. For incommensurate ground states, such as in $(\mathrm{TMTSF}{)}_{2}{\mathrm{PF}}_{6}$ the relaxation time distribution is homogeneously shifted to larger time when the duration of the heat input is increased, and exhibits, in addition, a scaling between the width and the position of the peak in the relaxation time distribution, ${w}^{2}\ensuremath{\sim}\mathrm{ln}({\ensuremath{\tau}}_{m})$. For a commensurate ground state, as in $(\mathrm{TMTTF}{)}_{2}{\mathrm{PF}}_{6}$, the relaxation time spectra show a bimodal character with a weight transfer between well separated slow and fast entities. Our interpretation is based on the dynamics of defects in the modulated structure, which depend crucially on the degree of commensurability.