Quantum Effects in Thermal Conductivity of Solid Krypton - Methane Solutions

TL;DR

This study investigates how quantum rotational effects of CH4 molecules influence the thermal conductivity of solid krypton solutions across various concentrations and temperatures, revealing resonance scattering, spin conversion effects, and a transition from quantum to classical rotation.

Contribution

It provides new insights into phonon-rotation interactions and the impact of nuclear spin and molecular anisotropy on thermal transport in quantum rotor-solvent systems.

Findings

Thermal conductivity exhibits a minimum influenced by nuclear spin conversion.

A sharp increase in thermal conductivity occurs around 8.4-9.7 K depending on CH4 concentration.

Anomalous temperature dependence indicates evolving phonon-rotation coupling.

Abstract

The dynamic interaction of a quantum rotor with its crystalline environment has been studied by measurement of the thermal conductivity of solid Kr1_c(CH4)_c solutions at c = 0.05-0.75 in the temperature region from 2 up to 40K. The thermal resistance of the solutions was mainly determined by the resonance scattering of phonons by CH4 molecules with the nuclear spin I=1 (the nuclear spin of T-species). The influence of the nuclear spin conversion on the temperature dependence of the thermal conductivity k(T) was found: a clearly defined minimum on k(T), its temperature position depending on the CH4 concentration. It was shown that the anisotropy molecular field not increase monotonously with the CH4 concentration. A compensation effect in the mutual orientation arrangement of the neighboring rotors is observed 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. The anomalous temperature dependence of the thermal resistance shows the evolution of the phonon-rotation coupling at varying temperature. It increases strongly when the character of CH4 rotation changes from the quantum at low temperatures to classical at high temperatures. Also, a jump of thermal conductivity (a sharp increase in k(T) within a narrow temperature range) was observed, whose position varies from 9.7 K to 8.4 K when the CH4 concentration changes from 0.25 to 0.45.