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

We present a study of the slow dynamics in the heat relaxation at very low temperature (T less than or similar to 1 K) in the nominally commensurate S DW compound (TMTTP)(2)Br, that we compare to the incommensurate SDW-(TMTSF) (2)PF6. Instead of a broad distribution of relaxation times g(log r) in the PF6 salt, the dynamics in the Br salt reveals almost "discrete hands" in t he relaxation spectrum. A saturation towards equilibrium is reached very ra pidly (within similar to 20 mn) at T similar to 100 mK in comparison with P F6 (more than 10 hr for the same temperature).