Probing angle dependent thermal conductivity in twisted bilayer MoSe2

TL;DR

This study investigates how twist angles in bilayer MoSe2 influence its thermal conductivity, revealing significant reductions due to moire superlattice effects and phonon scattering, supported by experimental and first-principles calculations.

Contribution

It provides the first detailed analysis of angle-dependent thermal conductivity in twisted bilayer MoSe2 using experimental Raman techniques and theoretical calculations.

Findings

Thermal conductivity varies with twist angle, from 13 to 30 W/mK.

Moire superlattice formation causes phonon scattering, reducing thermal conductivity.

Theoretical analysis confirms angle-dependent phonon behavior and localization effects.

Abstract

Twisted bilayer (t-BL) transition metal dichalcogenides (TMDCs) attracted considerable attention in recent years due to their distinctive electronic properties, which arise due to the moire superlattices that lead to the emergence of flat bands and correlated electron phenomena. Also, these materials can exhibit interesting thermal properties, including a reduction in thermal conductivity. In this article, we report the thermal conductivity of monolayer (1L) and t-BL MoSe2 at some specific twist angles around two symmetric stacking AB (0 degree) and AB' (60 degree) and one intermediate angle 31 (degree) using the optothermal Raman technique. The observed thermal conductivity values are found to be 13, 23, and 30 W m-1K-1 for twist angle = 58 (degree), 31 (degree) and, 3 (degree) respectively, which is well supported by our first-principles calculation results. The reduction in thermal conductivity in t-BL MoSe2 compared to monolayer (38 W m-1K-1) can be explained by the occurrence of phonon scattering caused by the formation of a moire super-lattice. Herein, the emergence of multiple folded phonon branches and modification in the Brillouin zone caused by in-plane rotation are also accountable for the decrease in thermal conductivity observed in t-BL MoSe2. The theoretical phonon lifetime study and electron localization function (ELF) analysis further reveals the origin of angle-dependent thermal conductivity in t-BL MoSe2. This work paves the way towards tuning the angle-dependent thermal conductivity for any bilayer TMDCs system.