engleski

Low temperature phonon thermal conductivity of the quasi-one-dimensional single crystals (Ta_1-xNb_xSe_4)_2I

We report on thermal conductivity measurements of the quasi-onedimensional single crystals (Ta_1-xNb_xSe_4)_2I (x=0, 0.008, 0.01) between 50 mK and 6 K. The thermal conductivity of a (TaSe_4)_2I sample obeys a cubic variation below 0.8 K, in good agreement with the boundary scattering regime. For two Nb doped samples, the thermal conductivity between 0.1 K and 1 K obeys a quasiquadratic regime, which is ascribed to extended "linear or planar defects", specific to this one-dimensional structure, and introduced either by doping or by successive thermal cycling, while it obeys a cubic variation below 0.1 K, as in the case of pure (TaSe_4)_2I. In the vicinity of 1 K and 2 K for pure and 1at.% Nb doped samples, thermal conductivity shows a very sharp peak, which exceeds the low-temperature cubic boundary Casimir regime, or the quasi quadratic regime, respectively. The presence of the peak in these systems is explained by a phonon Poiseuille flow, originating from their strong nharmonicity, amplified by the lattice anisotropy.

quasi-one dimensional compounds; phonon thermal conductivity; anharmonicity; phonon Poiseuille flow; scattering processes

nije evidentirano