谐振腔-单层二硫化钼系统中的高阶腔耦合等离极化激元

High-order cavity coupled plasmon polaritons in resonant cavity-monolayer MoS_(2) system

以单层MoS_(2)为代表的二维过渡金属硫族化物,因具有可调谐的非零带隙,故应用在光电子学器件中要比石墨烯更具优势.本文使用经典电磁理论和有限元分析方法,研究了谐振腔中腔模与单层MoS2等离激元之间耦合形成的腔耦合等离极化激元,并重点计算和验证了其中高阶模式的特性.考虑到化学气相沉积法生长的单层MoS_(2)中衬底、多晶和缺陷会引起弱电子局域化,从而导致基于自由电子气假设的Drude模型准确性变差,故本文在理论和仿真中使用了Drude-Smith模型描述单层MoS_(2)光电导率,该模型通过拟合实验数据得到.基于此,不仅导出了高阶腔耦合等离极化激元的色散方程,并求解出了其色散曲线,还通过仿真计算验证了这些高阶模式的存在性,分析了其基本性质以及弱电子局域化的影响.上述结果能加深对二维材料等离激元的耦合激发以及特性调控的理解,所用理论模型也能推广到其他低维、拓扑量子材料相关的等离系统当中.

Compared with graphene,two-dimensional(2D)transition metal sulfides,represented by mono-/few-layer MoS_(2),have tunable non-zero bandgap,and thus their applications in optoelectronic devices are more advantageous.By using classical electromagnetic theory and finite element method(FEM),we investigate the cavity coupled plasmon polaritons(CCPPs)formed through the coupling between cavity modes in a resonator and plasmons in monolayer MoS2,particularly calculate and verify the properties of the high-order CCPPs.In previous work,it was demonstrated that the substrates,defects,and polycrystalline grains of the CVD grown monolayer MoS_(2)usually induce weak electron localization,which leads to the deviation from the Drude model based on the approximation of free electron gas.Therefore,here we use the Drude-Smith model with characteristic parameters obtained experimentally to describe the optical conductivity of monolayer MoS_(2)in our theoretical calculation and simulation.Then,we not only derive and solve the dispersion equations of the high-order CCPPs,but also verify the existence and analyze the properties of these high-order modes.Specifically,there are three types of CCPPs in the asymmetric cavity-monolayer MoS_(2)system,i.e.the FP-like-modes(FPLMs),the surface-plasmon-like modes(SPLMs),and the quasi-localized modes(QLMs).Among them,the FPLMs and QLMs can support high-order modes whereas the SPLMs only support the fundamental modes.According to our model,we calculate the wave localization properties for the 7th-order and 8th-order FPLM,the 3rd-order and 6th-order QLM,and the SPLM.These theoretical results are in good agreement with the simulation results.Moreover,the effects of weak electron localization are also shown by comparing the field distributions of the CCPPs based on the Drude model with those based on the Drude-Smith model.It is found that weak electron localization can reduce the coupling between the cavity modes and the plasmons in monolayer MoS_(2).These results can deepen our understanding of the excitation of plasmons in 2D materials as well as the modulation of their properties.Furthermore,the theoretical model can also be extended to other plasmonic systems related to low-dimensional and topological quantum materials.