Radiatively Limited Dephasing and Exciton Dynamics in MoSe2 Monolayers Revealed with Four-Wave Mixing Microscopy.
Radiatively Limited Dephasing and Exciton Dynamics in MoSe2 Monolayers Revealed with Four-Wave Mixing Microscopy.
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DOI：
10.1021/acs.nanolett.6b01060
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发表时间：
2016-09-14
期刊：
影响因子：
10.8
通讯作者：
Kasprzak J
中科院分区：
文献类型：
--
作者：
Jakubczyk T;Delmonte V;Koperski M;Nogajewski K;Faugeras C;Langbein W;Potemski M;Kasprzak J
通过实施四波混频（FWM）显微光谱，我们测量的相干性和人口动力学的激子跃迁的MoSe 2单层。我们揭示了它们的退相时间T2和辐射寿命T1在亚皮秒（ps）范围内，接近T2 = 2 T1，从而表明在6 K的温度下辐射有限的退相。我们阐明的失相机制，通过改变温度，并通过探测不同的位置上表现出不同的局部混乱的薄片。在纳秒范围内，我们观察到的非相干激子，最初分散向暗态，但随后放松回到光锥内的光学活性状态产生的残余FWM。通过引入偏振分辨激发，我们推断谷间激子动力学，揭示了约30%的初始偏振度，恒定在初始亚皮秒衰减，其次是皮秒时间尺度上的去偏振。FWM高光谱成像揭示了样品的掺杂和未掺杂区域，使我们能够同时研究中性激子，带电激子或两者的跃迁。在后者中，我们观察到激子-激子在相干演化中的拍频，表明它们之间存在相干耦合。
By implementing four-wave mixing (FWM) microspectroscopy, we measure coherence and population dynamics of the exciton transitions in monolayers of MoSe2. We reveal their dephasing times T2 and radiative lifetime T1 in a subpicosecond (ps) range, approaching T2 = 2T1 and thus indicating radiatively limited dephasing at a temperature of 6 K. We elucidate the dephasing mechanisms by varying the temperature and by probing various locations on the flake exhibiting a different local disorder. At the nanosecond range, we observe the residual FWM produced by the incoherent excitons, which initially disperse toward the dark states but then relax back to the optically active states within the light cone. By introducing polarization-resolved excitation, we infer intervalley exciton dynamics, revealing an initial polarization degree of around 30%, constant during the initial subpicosecond decay, followed by the depolarization on a picosecond time scale. The FWM hyperspectral imaging reveals the doped and undoped areas of the sample, allowing us to investigate the neutral exciton, the charged one, or both transitions at the same time. In the latter, we observe the exciton–trion beating in the coherence evolution indicating their coherent coupling.
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