Probing angle-dependent thermal conductivity in twisted bilayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Mo</mml:mi><mml:msub><mml:mi>Se</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>

Abstract

Twisted bilayer (t-BL) transition-metal dichalcogenides (TMDCs) have attracted considerable attention in recent years due to their distinctive electronic properties, which arise due to the moir\'e 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 paper, we report the thermal conductivity of monolayer (1L) and t-BL $\mathrm{Mo}{\mathrm{Se}}_{2}$ at some specific twist angles around two symmetric stacking $\mathit{AB} ({0}^{\ensuremath{\circ}})$ and $A{B}^{\ensuremath{'}}$ (${60}^{\ensuremath{\circ}}$) and one intermediate angle $({31}^{\ensuremath{\circ}})$ using the optothermal Raman technique. The observed thermal conductivity values are found to be $13\ifmmode\pm\else\textpm\fi{}1, 23\ifmmode\pm\else\textpm\fi{}3$, and $30\ifmmode\pm\else\textpm\fi{}4\phantom{\rule{0.16em}{0ex}}{\mathrm{Wm}}^{\ensuremath{-}1\phantom{\rule{4pt}{0ex}}}{\mathrm{K}}^{\ensuremath{-}1}$ for twist angle $[\ensuremath{\theta}]={58}^{\ensuremath{\circ}}, {31}^{\ensuremath{\circ}}$, and ${3}^{\ensuremath{\circ}}$, respectively, which are well supported by our first-principles calculation results. The reduction in thermal conductivity in t-BL $\mathrm{Mo}{\mathrm{Se}}_{2}$ compared to monolayer $(38\ifmmode\pm\else\textpm\fi{}4\phantom{\rule{4pt}{0ex}}{\mathrm{Wm}}^{\ensuremath{-}1\phantom{\rule{4pt}{0ex}}}{\mathrm{K}}^{\ensuremath{-}1})$ can be explained by the occurrence of phonon scattering caused by the formation of a moir\'e superlattice. 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 $\mathrm{Mo}{\mathrm{Se}}_{2}$. The theoretical phonon lifetime study and electron localization function analysis further reveals the origin of angle-dependent thermal conductivity in t-BL $\mathrm{Mo}{\mathrm{Se}}_{2}$. This work paves the way towards tuning the angle-dependent thermal conductivity for any bilayer TMDCs system.

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