Valley-Coherent Hot Carriers and Thermal Relaxation in Monolayer Transition Metal Dichalcogenides

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• 作者：Sangeeth Kallatt ; Govindarao Umesh ; Kausik Majumdar
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2016
• 出版时间：June 2, 2016
• 年：2016
• 卷：7
• 期：11
• 页码：2032-2038
• 全文大小：537K
• 年卷期：0
• ISSN：1948-7185

文摘

We show room-temperature valley coherence in MoS₂, MoSe₂, WS₂, and WSe₂ monolayers using linear polarization-resolved hot photoluminescence (PL) at energies close to the excitation, demonstrating preservation of valley coherence before sufficient scattering events. The features of the copolarized hot luminescence allow us to extract the lower bound of the binding energy of the A exciton in monolayer MoS₂ as 0.42 (±0.02) eV. The broadening of the PL peak is found to be dominated by a Boltzmann-type hot luminescence tail, and using the slope of the exponential decay, the carrier temperature is extracted in situ at different stages of energy relaxation. The temperature of the emitted optical phonons during the relaxation process is probed by exploiting the corresponding broadening of the Raman peaks due to temperature-induced anharmonic effects. The findings provide a physical picture of photogeneration of valley-coherent hot carriers and their subsequent energy relaxation pathways.