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Low temperature phonon thermal conductivity of the quasi-one-dimensional compounds (NbSe4)3I, (TaSe4)2I and K0.3MoO3

We report on measurements of the thermal conductivity of quasi-one-dimensional compounds K0.3MoO3, (NbSe4)3I, and (TaSe4)2I between 0.07 K and 4 K. Despite the presence of a charge-density wave, the observed behaviour is similar to that expected in good insulating crystals, where the thermal conductivity well below 1 K is mainly governed by boundary scattering with some degree of specular reflection. However a pronounced anomaly is detected in (TaSe4)2I as a sharp maximum around 1 K, followed by a broad minimum around 3 K. We ascribe this anomaly to strong scattering by low-lying transverse acoustic phonons, with a very weak dispersion over a large part of the Brillouin zone, lying at an unusually low frequency.

low temperature phonon thermal conductivity; quasi-one-dimensional compounds; (NbSe4)3I; (TaSe4)2I; K0.3MoO3; charge-density wave; good insulating crystals; boundary scattering; specular reflection; low-lying transverse

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