Slow dynamics of energy relaxation in the commensurate SDW ground state of (TMTTF)2Br

We present a study, of the slow dynamics in the heat relaxation at very low temperature (T < 1 K) in the nominally commensurate SDW compound (TMTTF) 2 Br, that we compare to the incommensurate SDW-(TMTSF) 2 PF 6 . Instead of a broad distribution of relaxation times g(log τ) in the PF 6 salt, the dynamics in the Br salt reveals almost discrete bands in the relaxation spectrum. A saturation towards equilibrium is reached very rapidly (within ∼ 20 mn) at T ∼ 100 mK in comparison with PF 6 (more than 10 hr for the same temperature).