Renormalized Lattice Dynamics and Thermal Transport in VO$_{2}$

TL;DR

This study introduces a self-consistent phonon renormalization method to accurately model lattice dynamics and thermal transport in VO₂ across its metal-insulator transition, aligning well with experimental data.

Contribution

The paper develops a novel phonon renormalization scheme that captures temperature-dependent lattice vibrations and thermal conductivity in VO₂, highlighting the roles of magnetic and vibrational entropy.

Findings

Lattice thermal conductivity in rutile VO₂ is nearly temperature independent.

Thermal conductivity in monoclinic VO₂ varies inversely with temperature.

Rutile VO₂ exhibits substantially lower thermal conductivity due to phonon softening and scattering.

Abstract

Vanadium dioxide (VO$_{2}$) undergoes a first-order metal-insulator transition (MIT) upon cooling near room temperature, concomitant with structural change from rutile to monoclinic. Accurate characterization of lattice vibrations is vital for elucidating the transition mechanism. To investigate the lattice dynamics and thermal transport properties of VO$_{2}$ across the MIT, we present a phonon renormalization scheme based on self-consistent phonon theory through iteratively refining vibrational free energy. Using this technique, we compute temperature-dependent phonon dispersion and lifetimes, and point out the importance of both magnetic and vibrational entropy in driving the MIT. The predicted phonon dispersion and lifetimes show quantitative agreement with experimental measurements. We demonstrate that lattice thermal conductivity of rutile VO$_{2}$ is nearly temperature independent as a result of strong intrinsic anharmonicity, while that of monoclinic VO$_{2}$ varies according to $1/T$. Due to phonon softening and enhanced scattering rates, the lattice thermal conductivity is deduced to be substantially lower in the rutile phase, suggesting that Wiedemann-Franz law might not be strongly violated in rutile VO$_{2}$.