分类： 光学 >> 量子光学 提交时间： 2023-02-23
Hai Hu
Na Chen
Hanchao Teng
Renwen Yu
Yunpeng Qu
Jianzhe Sun
Mengfei Xue
Debo Hu
Bin Wu
Chi Li
Jianing Chen
Mengkun Liu
Zhipei Sun
Yunqi Liu
Peining Li
Shanhui Fan
F. Javier García de Abajo
Qing Dai
摘要： Controlling the charge carrier density provides an efficient way to trigger phase transitions and modulate the optoelectronic properties in natural materials. This approach could be used to induce topological transitions in the optical response of photonic systems. Here, we predict a topological transition in the isofrequency dispersion contours of hybrid polaritons supported by a two-dimensional heterostructure consisting of graphene and $\alpha$-phase molybdenum trioxide ($\alpha$-MoO3). By chemically changing the doping level of graphene, we experimentally demonstrate that the contour topology of polariton isofrequency surfaces transforms from open to closed shapes as a result of doping-dependent polariton hybridization. Moreover, by changing the substrate medium for the heterostructure, the dispersion contour can be further engineered into a rather flattened shape at the topological transition, thus supporting tunable polariton canalization and providing the means to locally control the topology. We demonstrate this idea to achieve extremely subwavelength focusing by using a 1.2-$\mu$m-wide silica substrate as a negative refraction lens. Our findings open a disruptive approach toward promising on-chip applications in nanoimaging, optical sensing, and manipulation of nanoscale energy transfer.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Longlong Yang
Xin Xie
Jingnan Yang
Mengfei Xue
Shiyao Wu
Shan Xiao
Feilong Song
Jianchen Dang
Sibai Sun
Zhanchun Zuo
Jianing Chen
Yuan Huang
Xingjiang Zhou
Kuijuan Jin
Can Wang
Xiulai Xu
摘要： Strong exciton-plasmon interaction between the layered two-dimensional (2D) semiconductors and gap plasmons shows a great potential to implement cavity quantum-electrodynamics in ambient condition. However, achieving a robust plasmon-exciton coupling with nanocavity is still very challenging, because the layer area is usually small with conventional approaches. Here, we report on a robust strong exciton-plasmon coupling between the gap mode of bowtie and the excitons in MoS$_2$ layers with gold-assisted mechanical exfoliation and the nondestructive wet transfer techniques for large-area layer. Benefiting from the ultrasmall mode volume and strong in-plane field, the estimated effective exciton number contributing to the coupling is largely reduced. With a corrected exciton transition dipole moment, the exciton numbers are extracted with 40 for the case of monolayer and 48 for 8 layers. Our work paves a way to realize the strong coupling with 2D materials with few excitons at room temperature.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Hai Hu
Na Chen
Hanchao Teng
Renwen Yu
Mengfei Xue
Ke Chen
Yuchuan Xiao
Yunpeng Qu
Debo Hu
Jianing Chen
Zhipei Sun
Peining Li
F. Javier García de Abajo
Qing Dai
摘要： Negative refraction provides an attractive platform to manipulate mid-infrared and terahertz radiation for molecular sensing and thermal radiation applications. However, its implementation based on available metamaterials and plasmonic media presents challenges associated with optical losses, limited spatial confinement, and lack of active tunability in this spectral range. Here, we demonstrate gate-tunable negative refraction at mid-infrared frequencies using hybrid topological polaritons in van der Waals heterostructures with high spatial confinement. We experimentally visualize wide-angle negatively-refracted surface polaritons on {\alpha}-MoO3 films partially decorated with graphene, undergoing planar nanoscale focusing down to 1.6% of the free-space wavelength. Our atomically thick heterostructures outperform conventional bulk materials by avoiding scattering losses at the refracting interface while enabling active tunability through electrical gating. We propose polaritonic negative refraction as a promising platform for infrared applications such as electrically tunable super-resolution imaging, nanoscale thermal manipulation, and molecular sensing.
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