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Single-Nanoparticle Plasmonic Electro-optic Modulator Based on MoS2 Monolayers Bowen Li,?,§ Shuai Zu,?,§ Jiadong Zhou,? Qiao Jiang,? Bowen Du,? Hangyong Shan,? Yang Luo,? Zheng Liu,? Xing Zhu,? and Zheyu Fang*,? ? School of Physics, State Key Lab for Mesoscopic Physics;

Academy for Advanced Interdisciplinary Studies;

Collaborative Innovation Center of Quantum Matter, Peking University, Beijing 100871, China ? Center for Programmable Materials, School of Electrical and Electronic Engineering, Nanyang Technology University, Singapore

639798 * S Supporting Information ABSTRACT: The manipulation of light in an integrated circuit is crucial for the development of high-speed electro-optic devices.

Recently, molybdenum disul?de (MoS2) monolayers generated broad interest for the optoelectronics because of their huge exciton binding energy, tunable optical emission, direct electronic band-gap structure, etc. Miniaturization and multifunctionality of electro-optic devices further require the manipulation of light?matter interaction at the single-nanoparticle level. The strong exciton?plasmon interaction that is generated between the MoS2 monolayers and metallic nanostructures may be a possible solution for compact electro-optic devices at the nanoscale. Here, we demonstrate a nanoplasmonic modulator in the visible spectral region by combining the MoS2 monolayers with a single Au nanodisk. The narrow MoS2 excitons coupled with broad Au plasmons result in a deep Fano resonance, which can be switched on and o? by applying di?erent gate voltages on the MoS2 monolayers. A reversible display device that is based on this single-nanoparticle modulator is demonstrated with a heptamer pattern that is actively controlled by the external gates. Our work provides a potential application for electro-optic modulation on the nanoscale and promotes the development of gate-tunable nanoplasmonic devices in the future. KEYWORDS: MoS2, exciton?plasmon interaction, electro-optic modulator, Fano resonance, trions Plasmonics and transition metal dichalcogenides (TMDCs) are two of the most rapidly advancing research areas in nanophononics.1?4 Surface plasmons, with properties of nanoscale light con?nement5 and electro- magnetic ?eld enhancement,6 have induced great applications in plasmonic focusing,7 integrated waveguides,8 active modu- lation,9,10 hot electron photodetection,11 etc. Plasmonic Fano resonance, as a coherent scattering phenomenon with an asymmetric line shape, is caused by the interference between a bright broad mode and a dark narrow state,12 which has been widely used for biosensing,13 optical switching,14 and electro- magnetically induced transparency.15 Recently, the Fano resonance was further investigated by using a metallic nanostructure interacting with semiconducting quantum dots, where the strong coupling between the plasmon and exciton can generate a so-called plexciton resonance,16,17 which provides potential applications for the quantum optical device. Meanwhile, the extraordinary properties of TMDC materials have generated great interest in the optoelectronics commun- ity.18?20 Molybdenum disul?de (MoS2) monolayers have attracted tremendous interest in recent years because of their direct electronic band-gap structure,21?24 versatile optical transitions,25?27 and tunable mechanical properties.28,29 More- over, tightly bound excitons in the MoS2 monolayers make it a good candidate for fundamental physical studies and provide a signi?cant opportunity to realize an electro-optic device that operates in the visible spectral region.26,30?34 The combination of plasmonic nanostructures with MoS2 monolayers shows a great application potential.23,27,35 The strong electromagnetic ?eld associated with the localized surface plasmon (LSP) resonance can be con?ned to the deep subwavelength space. Depositing metallic nanostructures onto the MoS2 monolayers can realize a stronger light?matter interaction36?39 and has been used to produce signi?cant advances for the photovoltaics,38 photodetection,40,41 and sensing.42 On the other side, the tightly bound trions (quasi- particles composed of two electrons and a hole) and excitons of the MoS2 monolayers can be tuned by electrical doping, which Received: August 1,