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 (.L). Here, we report the ultralow.L in the monolayer tellurium, i. e., tellurene, which has been successfully synthesized in recent experiments. We find that tellurene has a compellingly low room temperature.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.L to the soft acoustic modes, the extremely low-energy optical modes and the strong scattering among optical-acoustic phonons, which place tellurene as a potential novel thermoelectric material. Finally, we show that.L is proportional to the largest acoustic phonon frequency (.a D) and the lowest optical phonon frequency at the G point (.oG) in 2D materials, which reflect both harmonic and anharmonic thermal properties, respectively.