Sun Liuyang, Kumar Parveen, Liu Zeyu, Choi Junho, Fang Bin, Roesch Sebastian, Tran Kha, Casara Joshua, Priego Eduardo, Chang Yu-Ming, Moody Galan, Silverman Kevin L, Lorenz Virginia O, Scheibner Michael, Luo Tengfei, Li Xiaoqin
Department of Physics, The University of Texas at Austin, Austin, Texas 78712, United States.
Department of Physics, University of California Merced, Merced, California 95340, United States.
Nano Lett. 2021 Feb 10;21(3):1434-1439. doi: 10.1021/acs.nanolett.0c04368. Epub 2021 Jan 28.
A variety of quantum degrees of freedom, e.g., spins, valleys, and localized emitters, in atomically thin van der Waals materials have been proposed for quantum information applications, and they inevitably couple to phonons. Here, we directly measure the intrinsic optical phonon decoherence in monolayer and bulk MoS by observing the temporal evolution of the spectral interference of Stokes photons generated by pairs of laser pulses. We find that a prominent optical phonon mode E exhibits a room-temperature dephasing time of ∼7 ps in both the monolayer and bulk. This dephasing time extends to ∼20 ps in the bulk crystal at ∼15 K, which is longer than previously thought possible. First-principles calculations suggest that optical phonons decay via two types of three-phonon processes, in which a pair of acoustic phonons with opposite momentum are generated.
原子级薄的范德华材料中的各种量子自由度，如自旋、谷和局域发射体，已被提出用于量子信息应用，并且它们不可避免地与声子耦合。在此，我们通过观察由激光脉冲对产生的斯托克斯光子的光谱干涉的时间演化，直接测量了单层和体相MoS中的本征光学声子退相干。我们发现，一个显著的光学声子模式E在单层和体相中均表现出约7 ps的室温退相时间。在约15 K的体相晶体中，该退相时间延长至约20 ps，这比之前认为可能的时间更长。第一性原理计算表明，光学声子通过两种类型的三声子过程衰变，其中产生一对具有相反动量的声子。
