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Unusually low thermal conductivity of atomically thin 2D tellurium

Tellurium is a high-performance thermoelectric material due to its superior electronic transport and low lattice thermal conductivity ($κ_L$). Here, we report the ultralow $κ_L$ in the monolayer tellurium, i.e., tellurene, which has been successfully synthesized in recent experiments. We find tellurene has a compellingly low room temperature $κ_L$ of 2.16 and 4.08 W m$^{-1}$ K$^{-1}$ along the armchair and zigzag directions, respectively, which is lower than any reported values for other 2D materials. We attribute this unusually low $κ_L$ to the soft acoustic modes, extremely low-energy optical modes and the strong scattering among optical-acoustic phonons, which place tellurene as a potential novel thermoelectric material. Finally, we disclose that $κ_L$ is proportional to the largest acoustic phonon frequency ($ω_{D}^{a}$) and the lowest optical phonon frequency at $Γ$ point ($ω_Γ^{o}$) in 2D materials, which reflect both harmonic and anharmonic thermal properties respectively.