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Effects of Excitonic Resonance on Second and Third Order Nonlinear Scattering from Few-Layer MoS2
ACS Photonics ( IF 6.5 ) Pub Date : 2018-01-25 00:00:00 , DOI: 10.1021/acsphotonics.7b00912 Naveen K. Balla 1 , Maria O’Brien , Niall McEvoy , Georg S. Duesberg 2 , Hervé Rigneault 1 , Sophie Brasselet 1 , David McCloskey
ACS Photonics ( IF 6.5 ) Pub Date : 2018-01-25 00:00:00 , DOI: 10.1021/acsphotonics.7b00912 Naveen K. Balla 1 , Maria O’Brien , Niall McEvoy , Georg S. Duesberg 2 , Hervé Rigneault 1 , Sophie Brasselet 1 , David McCloskey
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Nonlinear optical scattering from single- and few-layer MoS2 contains important information about the orientation, inversion symmetry, and degree of interlayer coupling between the layers. We simultaneously map second harmonic generation (SHG) and four wave mixing (FWM) signals in chemical vapor deposition (CVD) grown 2H-phase MoS2 from single to five layers. We tune the excitation wavelengths to compare cases where the nonlinear signals are on and off resonance with the A-exciton band. The SHG signal shows the expected 4-fold symmetry, however, the FWM signal depends on the incident laser polarization only, and is independent of the crystallographic orientation. We show using the symmetry of the χ(3) tensor that this results from out of plane FWM dipoles. We explore the scaling of SHG and FWM signals with layer number on and off excitonic resonance When a nonlinear scattered signal overlaps with the A excitonic band, the scaling of the signals with layer number deviates from the expected values, due to the layer dependent red shift in the exciton absorption peak due to interlayer coupling. Finally we show that circularly polarized excitation significantly enhances nonlinear scattering which overlaps with the A excitonic band and indicates the presence of spin splitting of valence bands at the energy degenerate points (K, K′) of the Brillouin zone.
中文翻译：
激子共振对少量MoS 2的二阶和三阶非线性散射的影响
来自单层和少层MoS 2的非线性光学散射包含有关方向，反演对称性以及各层之间层间耦合程度的重要信息。我们在从单层到五层的化学气相沉积（CVD）生长的2H相MoS 2中同时映射了二次谐波生成（SHG）和四波混合（FWM）信号。我们调整激发波长，以比较非线性信号在A-激子带上共振的情况。SHG信号显示出预期的4倍对称性，但是FWM信号仅取决于入射激光偏振，并且与晶体取向无关。我们展示了使用χ （3）的对称性张量，这是由平面外FWM偶极子引起的。我们探索具有开和关激子共振层数的SHG和FWM信号的缩放比例当非线性散射信号与A激子谱带重叠时，由于层数依赖于红移，具有层数的信号的缩放比例会偏离预期值由于层间耦合，在激子吸收峰中的峰。最后，我们表明，圆极化激发显着增强了非线性散射，该散射与A激子能带重叠，并表明在布里渊区的能量简并点（K，K '）上存在价带自旋分裂的存在。
更新日期：2018-01-25
中文翻译：
激子共振对少量MoS 2的二阶和三阶非线性散射的影响
来自单层和少层MoS 2的非线性光学散射包含有关方向，反演对称性以及各层之间层间耦合程度的重要信息。我们在从单层到五层的化学气相沉积（CVD）生长的2H相MoS 2中同时映射了二次谐波生成（SHG）和四波混合（FWM）信号。我们调整激发波长，以比较非线性信号在A-激子带上共振的情况。SHG信号显示出预期的4倍对称性，但是FWM信号仅取决于入射激光偏振，并且与晶体取向无关。我们展示了使用χ （3）的对称性张量，这是由平面外FWM偶极子引起的。我们探索具有开和关激子共振层数的SHG和FWM信号的缩放比例当非线性散射信号与A激子谱带重叠时，由于层数依赖于红移，具有层数的信号的缩放比例会偏离预期值由于层间耦合，在激子吸收峰中的峰。最后，我们表明，圆极化激发显着增强了非线性散射，该散射与A激子能带重叠，并表明在布里渊区的能量简并点（K，K '）上存在价带自旋分裂的存在。
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