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Helicity‐resolved resonant Raman spectroscopy of layered WS2
Journal of Raman Spectroscopy ( IF 2.5 ) Pub Date : 2020-09-22 , DOI: 10.1002/jrs.5996
Yan Zhao 1, 2 , Shiyi Han 2 , Jin Zhang 2 , Lianming Tong 2
Affiliation  

When excited by circularly polarized light, the Raman scattered light may have the same or opposite helicity as the incident light determined by the helicity selection rule. For two‐dimensional (2D) transition metal dichalcogonides (TMDCs), the helicity selection rule can be broken down due to the strong Fröhlich exciton–phonon interaction. However, how the helicity selection rule changes with excitation energy has not been reported yet. Here, we study the helicity‐resolved Raman scattering of layered WS2 excited by circularly polarized light for excitations off‐excitonic resonance and near resonance to different excitons. We find that for off‐resonance excitation, the helicity of urn:x-wiley:03770486:media:jrs5996:jrs5996-math-0003 mode of WS2 obeys the helicity selection rule determined by the symmetry of crystal structure and vibration modes. When excited near resonance to the B exciton, the breakdown of the helicity selection rule is observed, which is attributed to the appearance of nonzero diagonal elements of the Raman tensor resulted from the Fröhlich exciton–phonon interaction. The layer number dependence of the helicity polarization ratio of the urn:x-wiley:03770486:media:jrs5996:jrs5996-math-0004 mode shows that the proportion of helicity‐conserved component decreases with the increase of layer number. When the excitation energy is near resonance to the A exciton, the different helicity polarization ratio is found and remains unchanged with increasing layer number, which may be attributed to the different coupling strengths of exciton–phonon interactions.

中文翻译:

分层WS2的螺旋分辨共振拉曼光谱

当由圆偏振光激发时,拉曼散射光可以具有与通过螺旋度选择规则确定的入射光相同或相反的螺旋度。对于二维(2D)过渡金属双金属双氰胺(TMDC),由于强烈的Fröhlich激子-声子相互作用,可以打破螺旋选择规则。然而,尚未报道螺旋度选择规则如何随着激发能量而变化。在这里,我们研究了圆偏振光激发的层状WS 2的螺旋分辨拉曼散射,用于激发不同激发子的非激子共振和近共振。我们发现,对于非共振激发,骨灰盒:x-wiley:03770486:media:jrs5996:jrs5996-math-0003WS 2模式的螺旋度遵守由晶体结构和振动模式的对称性决定的螺旋度选择规则。当在B激子的共振附近激发时,观察到螺旋选择规则的破坏,这是由于Fröhlich激子-声子相互作用导致拉曼张量的非零对角元素的出现。该骨灰盒:x-wiley:03770486:media:jrs5996:jrs5996-math-0004模式的螺旋极化率的层数依赖性表明,随着层数的增加,保留螺旋度的组分所占的比例降低。当激发能量接近于A激子共振时,发现了不同的螺旋极化率,并且随着层数的增加而保持不变,这可能是由于激子-声子相互作用的耦合强度不同所致。
更新日期:2020-09-22
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