Slow energy relaxation at low temperature in quasi-1D organic conductors

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 (TMTTF)(2)Br, that we compare to the incommensurate SDW-(TMTSF) (2)PF6. Instead of a broad distribution of relaxation times g (log tau) in the PF6 salt typical of glassy materials, the dynamics in the Br salt revea ls almost "discrete bands" in the relaxation spectrum. A saturation towards equilibrium is reached very rapidly (within similar to 20 mn) at T similar to 100 mK in comparison with PF6 (more than a few days for the same temper ature).