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

We show that the low temperature (T<0.5 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 (TMTSF)₂PF₆ 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, w²∼ln((τ_m). For a commensurate ground state, as in (TMTTF)₂PF₆, 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.