Acoustic phonon-restricted four-phonon interactions: Impact on thermal and thermoelectric transport in monolayer h-NbN

TL;DR

This study investigates how four-phonon interactions influence heat and thermoelectric transport in monolayer h-NbN, revealing the importance of acoustic phonons and strain effects in optimizing thermoelectric performance.

Contribution

It provides a detailed first-principles analysis of four-phonon interactions and their impact on thermal and thermoelectric properties in monolayer h-NbN, highlighting strain effects.

Findings

Four-phonon interactions mainly affect acoustic phonons.

Strain reduces anharmonicity and enhances thermal conductivity.

Thermoelectric figure of merit approaches 1 at high temperatures.

Abstract

To explore the thermal and thermoelectric potential of 2D materials, we study the h-NbN monolayer, which lacks mirror symmetry and features a large acoustic-optical phonon gap and quadratic flexural mode. First-principles calculations and the Boltzmann transport formalism reveal a complex interplay of multi-phonon scattering processes, where flexural phonons and four-phonon interactions play a significant role in heat transport, primarily dominated by acoustic phonons. Notably, the four-phonon interactions are predominantly confined to acoustic phonons. Tensile strain preserves the underlying scattering mechanisms while reducing anharmonicity, consequently, the scattering rates, enhancing thermal conduction. Simultaneously, competing modifications in thermal and electrical transport shape the strain-dependent thermoelectric response, achieving a figure of merit approaching 1 at elevated temperatures, a testament to its thermoelectric promise. Our findings underscore the critical role of microscopic transport modeling in accurately capturing thermal and thermoelectric properties, paving the way for advanced applications of 2D materials.