Low-frequency dynamics in molecular incommensurate composite: Specific heat of nonadecane/urea inclusion compound

We report the first very low-temperature specific-heat data of the incommensurate n-nonadecane/urea inclusion compound. In addition to the contribution due to normal acoustic phonons, the results show a linear temperature? dependence of the specific heat below 1.5 K, assigned to the dynamical disorder of the guest molecules. The excess heat capacity around 4.5 K reveals the low-frequency contribution of nondispersive modes. In contrast to the case of modulated incommensurate compounds, no pinned sliding?; mode, phasan-like mode, could be detected.