Explanation of the glasslike anomaly in the low-temperature specific heat of incommensurate phases.

An explanation of the glasslike anomaly observed in the low-temperature specific heat of incommensurate phases is proposed. The key point of this explanation is to properly account for the phason damping when computing the thermodynamic magnitudes. The low-temperature specific heat of the incommensurate phases is discussed within three possible scenarios for the phason dynamics: no phason gap, static phason gap, and a phason gap of dynamical origin. Existing NMR and inelastic scattering data indicate that these scenarios are possible in biphenyl, blue bronze K(0.30)MoO(3), and bis (4-chlorophenyl) sulfone respectively. Estimates of the corresponding low-temperature specific heat are in reasonable agreement with the experiments.