Li Ziwei, Liu Changxu, Rong Xin, Luo Yang, Cheng Haotian, Zheng Liheng, Lin Feng, Shen Bo, Gong Yongji, Zhang Shuang, Fang Zheyu
State Key Lab for Mesoscopic Physics, School of Physics, and Collaborative Innovation, Center of Quantum Matter, Peking University, Beijing, 100871, China.
Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, 100871, China.
Adv Mater. 2018 Jul 8:e1801908. doi: 10.1002/adma.201801908.
Transition metal dichalcogenides with intrinsic spin-valley degrees of freedom hold great potentials for applications in spintronic and valleytronic devices. MoS monolayer possesses two inequivalent valleys in the Brillouin zone, with each valley coupling selectively with circularly polarized photons. The degree of valley polarization (DVP) is a parameter to characterize the purity of valley-polarized photoluminescence (PL) of MoS monolayer. Usually, the detected values of DVP in MoS monolayer show achiral property under optical excitation of opposite helicities due to reciprocal phonon-assisted intervalley scattering process. Here, it is reported that valley-polarized PL of MoS can be tailored through near-field interaction with plasmonic chiral metasurface. The resonant field of the chiral metasurface couples with valley-polarized excitons, and tailors the measured PL spectra in the far-field, resulting in observation of chiral DVP of MoS -metasurface under opposite helicities excitations. Valley-contrast PL in the chiral heterostructure is also observed when illuminated by linearly polarized light. The manipulation of valley-polarized PL in 2D materials using chiral metasurface represents a viable route toward valley-polaritonic devices.
具有本征自旋谷自由度的过渡金属二硫属化物在自旋电子学和谷电子学器件中具有巨大的应用潜力。单层MoS₂在布里渊区拥有两个不等价的谷，每个谷与圆偏振光子选择性耦合。谷极化度（DVP）是表征单层MoS₂谷极化光致发光（PL）纯度的一个参数。通常，由于相互作用的声子辅助谷间散射过程，在相反螺旋度的光激发下，单层MoS₂中检测到的DVP值显示出非手性特性。在此，据报道，MoS₂的谷极化PL可以通过与等离子体手性超表面的近场相互作用来调控。手性超表面的共振场与谷极化激子耦合，并在远场中调整测量的PL光谱，从而在相反螺旋度激发下观察到MoS₂-超表面的手性DVP。当用线偏振光照射时，在手性异质结构中也观察到了谷对比度PL。使用手性超表面对二维材料中的谷极化PL进行调控，是通往谷极化子器件的一条可行途径。
