Low temperature specific heat of blue bronze K 0.30 MoO 3

Abstract

We report on specific heat measurements of the quasi-one-dimensional model system blue bronze K0.3MoO3, performed over a wide temperature interval 0.1-30 K, in its charge density wave (CDW) ground state. In this T range, the specific heat is successively determined by the presence of low-energy excitations (LEE) due to the disordered nature of the CDW ground-state, the acoustical phonon contribution which obeys an exact T3 law between 0.7 and 3.5 K, and a large excess of C / T 3 centered at 11.5-13 K. The contribution of the LEEs is of particularly low amplitude in comparison to other CDW systems. Also, feeble time-dependent effects could be detected. This implies a less disordered ground state in this compound. The C / T 3 bump, mainly of phononic origin, can be partly ascribed to a phason-excitation contribution, with a low-energy cut-off defined by the pinning energy. This interpretation is supported by the sensitivity of the low-T side of the bump to the purity of samples, and therefore to their pinning frequency. A similar effect was already measured in the specific heat of the CDW compound (TaSe4)2I, by comparison between pure and doped samples. Finally, we outline once more that some generic thermodynamic properties of CDW systems are similar to structurally disordered systems.