摘要
We investigate the microscopic mechanism of ultralow lattice thermal conductivity(κl)of TlInTe_(2)and its weak temperature dependence using a unified theory of lattice heat transport,that considers contributions arising from the particle-like propagation as well as wave-like tunneling of phonons.While we use the Peierls–Boltzmann transport equation(PBTE)to calculate the particlelike contributions(κl(PBTE)),we explicitly calculate the off-diagonal(OD)components of the heat-flux operator within a firstprinciples density functional theory framework to determine the contributions(κl(OD))arising from the wave-like tunneling of phonons.At each temperature,T,we anharmonically renormalize the phonon frequencies using the self-consistent phonon theory including quartic anharmonicity,and utilize them to calculateκl(PBTE)andκl(OD).With the combined inclusion ofκl(PBTE),κl(OD),and additional grain-boundary scatterings,our calculations successfully reproduce the experimental results.Our analysis shows that large quartic anharmonicity of TlInTe_(2)(a)strongly hardens the low-energy phonon branches,(b)diminishes the three-phonon scattering processes at finite T,and(c)recovers the weaker than T^(−1) decay of the measuredκl.
基金
We acknowledgefinancial supports from the Department of Energy,Office of Science,Basic Energy Sciences under grant DE-SC0014520 and the U.S.Department of Commerce and National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design(CHiMaD)under award no.70NANB14H012(DFT calculations).
