  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.
