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 <or∼ 1 K) in the nominally commensurate SDW compound (TMTTF)2Br, that we compare to the incommensurate SDW-(TMTSF)2PF6. Instead of a broad distribution of relaxation times g(log τ) in the PF6 salt typical of glassy materials, 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 PF6 (more than a few days for the same temperature). (orig.)