Quantum effects in the thermal conductivity of solid krypton—methane solutions

Abstract

The dynamic interaction of a quantum rotor with its crystalline environment has been studied by measurement of the thermal conductivity of the Kr₁–c(CH₄)c solid solutions at c = 0.05–0.75 in the temperature region 2–40 K. The thermal resistance of the solutions was mainly determined by the resonance scattering of phonons on CH₄ molecules with the nuclear spin I = 1 (the nuclear spin of the T species). The influence of the nuclear spin conversion on the temperature dependence of the thermal conductivity к(T) leads to a well-defined minimum on к(T). The temperature of the minimum depends on the CH₄ concentration. It was shown that the nonmonotonic increase of the anisotropic molecular field with the CH₄ concentration is caused by a compensation effect due to corrections in the mutual orientations of the neighboring rotors at c > 0.5. The temperature dependence of Kr₁–c(CH₄)c is described within the Debye model of thermal conductivity taking into account the lower limit of the phonon mean free path. It is shown that phonon–rotation coupling is responsible for the anomalous temperature dependence of the thermal resistance at varying temperature. It increases strongly when the quantum character of the CH₄ rotation at low temperatures changes to a classical one at high temperatures. A thermal conductivity jump (a sharp increase in к(T) within a narrow temperature range) was also observed. The temperature position of the jump varies from 9.7 to 8.4 K when the CH₄ concentration changes from 0.25 to 0.45.