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首页> 外文期刊>Physical Review X >Exciton States in Monolayer MoSe 2 and MoTe 2 Probed by Upconversion Spectroscopy
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Exciton States in Monolayer MoSe 2 and MoTe 2 Probed by Upconversion Spectroscopy

机译：通过上转换光谱探测的单层MOSE 2和MOTE 2中的激子状态

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Transitions metal dichalcogenides (TMDs) are direct gap semiconductors in the monolayer (ML) limit with fascinating optical and spin-valley properties. The strong optical absorption of up to 20% for a single ML is governed by excitons, electron-hole pairs bound by Coulomb attraction. Excited exciton states in MoSe 2 and MoTe 2 monolayers have so far been elusive because of their low oscillator strength and strong inhomogeneous broadening. Here, we show that encapsulation in hexagonal boron nitride results in an emission line width of the A : 1 s exciton below 1.5?meV and 3?meV in our MoSe 2 and MoTe 2 monolayer samples, respectively. This allows us to investigate the excited exciton states by photoluminescence upconversion spectroscopy for both monolayer materials. The excitation laser is tuned into resonance with the A : 1 s transition, and we observe emission of excited exciton states up to 200?meV above the laser energy. We demonstrate bias control of the efficiency of this nonlinear optical process. We discuss the origin of the upconversion effect. Our model calculations suggest an exciton-exciton (Auger) scattering mechanism specific to TMD MLs involving an excited conduction band, thus generating high-energy excitons with small wave vectors. The optical transitions are further investigated by white light reflectivity, photoluminescence excitation, and resonant Raman scattering, confirming their origin as excited excitonic states in monolayer thin semiconductors.
机译：过渡金属二均甲基化物（TMDS）是单层（ML）中的直接间隙半导体，具有迷人的光学和旋转谷属性。对于单毫升的强光学吸收高达20％由Excitons，由库仑吸引的电子孔对。由于它们的低振荡器强度和强烈的不均匀扩大，所以兴奋的激子状态在MOSE 2和MOTE 2单层的令人难以捉摸。在这里，我们表明，六边形氮化物中的封装导致A：1 S激子的排放线宽，低于1.5？MEV和3？MEV分别在我们的系统2中，并分别在2号单层样品中。这允许我们通过用于单层材料的光致发光上转化光谱来研究激发激子状态。激光激光与A：1秒的过渡调谐成共振，我们观察激发激子状态的发射高达200°的激光能量。我们展示了对该非线性光学过程效率的偏差控制。我们讨论了上翻效应的起源。我们的模型计算表明了一种特定于涉及激发传导带的TMD MLS的激子激励（螺旋钻）散射机构，从而产生具有小波形矢量的高能量激子。通过白光反射率，光致发光激发和共振拉曼散射进一步研究光学转变，以单层薄半导体在单层薄半导体中确认它们的起源。

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