# Thermal conductivity and phonon hydrodynamics in transition metal dichalcogenides from first-principles

## TL;DR

This study uses first-principles calculations to analyze thermal conductivity and phonon hydrodynamics in monolayer transition metal dichalcogenides, revealing significant hydrodynamic effects comparable to graphene, especially in WSe₂ at high temperatures.

## Contribution

It systematically compares theoretical frameworks for solving the Boltzmann Transport Equation beyond RTA in TMDs, highlighting the importance of accurate methods for predicting thermal properties.

## Key findings

- RTA underpredicts thermal conductivity in MS₂ materials.
- Hydrodynamic effects are significant in TMDs, similar to graphene.
- WSe₂ shows prominent hydrodynamic behavior at high temperatures.

## Abstract

We carry out a systematic study of the thermal conductivity of four single-layer transition metal dichalcogenides, MX$_2$ (M = Mo, W; X = S, Se) from first-principles by solving the Boltzmann Transport Equation (BTE). We compare three different theoretical frameworks to solve the BTE beyond the Relaxation Time Approximation (RTA), using the same set of interatomic force constants computed within density functional theory (DFT), finding that the RTA severely underpredicts the thermal conductivity of MS$_2$ materials. Calculations of the different phonon scattering relaxation times of the main collision mechanisms and their corresponding mean free paths (MFP) allow evaluating the expected hydrodynamic behaviour in the heat transport of such monolayers. These calculations indicate that despite of their low thermal conductivity, the present TMDs can exhibit large hydrodynamic effects, being comparable to those of graphene, especially for WSe$_2$ at high temperatures.