Ultrahigh lattice thermal conductivity in topological semimetal TaN caused by large acoustic-optical gap

TL;DR

This study predicts ultrahigh lattice thermal conductivity in topological semimetal TaN, attributed to a large acoustic-optical phonon gap that suppresses scattering, making it promising for heat dissipation in nano-electronics.

Contribution

It reveals the origin of high thermal conductivity in TaN due to phonon lifetime enhancement from a large acoustic-optical gap, a novel insight for topological semimetals.

Findings

TaN has anisotropic thermal conductivity of 838.62 and 1080.40 W/mK.

Phonon lifetimes in TaN are significantly longer than in other topological semimetals.

Large atomic mass difference in TaN creates a big acoustic-optical gap, reducing phonon scattering.

Abstract

Topological semimetal may have potential applications like topological qubits, spintronics and quantum computations. Efficient heat dissipation is a key factor for the reliability and stability of topological semimetal-based nano-electronics devices, which is closely related to high thermal conductivity. In this work, the elastic properties and lattice thermal conductivity of TaN are investigated by first-principles calculations and the linearized phonon Boltzmann equation within the single-mode relaxation time approximation (RTA). According to the calculated bulk modulus, shear modulus and $C_{44}$, TaN can be regarded as a potential incompressible and hard material. The room-temperature lattice thermal conductivity is predicted to be 838.62 $\mathrm{W m^{-1} K^{-1}}$ along a axis and 1080.40 $\mathrm{W m^{-1} K^{-1}}$ along c axis, showing very strong anisotropy. It is found that the lattice thermal conductivity of TaN is several tens of times higher than one of other topological semimetal, such as TaAs, MoP and ZrTe, which is due to very longer phonon lifetimes for TaN than other topological semimetal. The very different atomic masses of Ta and N atoms lead to a very large acoustic-optical band gap, and then prohibits the scattering between acoustic and optical phonon modes, which gives rise to very long phonon lifetimes. Based on mass difference factor, the WC and WN can be regarded as potential candidates with ultrahigh lattice thermal conductivity. Calculated results show that isotope scattering has little effect on lattice thermal conductivity, and that phonon with mean free path(MFP) larger than 20 (80) $\mathrm{\mu m}$ at 300 K has little contribution to the total lattice thermal conductivity. This work implies that TaN-based nano-electronics devices may be more stable and reliable due to efficient heat dissipation.