Browsing by Author "Teng, Hanchao"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Active control of micrometer plasmon propagation in suspended graphene
    (Nature Publishing Group, 2022-03-18) Hu, Hai; Yu, Renwen; Teng, Hanchao; Hu, Debo; Chen, Na; Qu, Yunpeng; Yang, Xiaoxia; Chen, Xinzhong; McLeod, A. S.; Alonso-González, Pablo; Guo, Xiangdong; Li, Chi; Yao, Ziheng; Li, Zhenjun; Chen, Jianing; Sun, Zhipei; Liu, Mengkun; García de Abajo, F. Javier; Dai, Qing; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; National Center for Nanoscience and Technology Beijing; Barcelona Institute of Science and Technology; Stony Brook University; Columbia University; University of Oviedo; CAS - Institute of Physics
    Due to the two-dimensional character of graphene, the plasmons sustained by this material have been invariably studied in supported samples so far. The substrate provides stability for graphene but often causes undesired interactions (such as dielectric losses, phonon hybridization, and impurity scattering) that compromise the quality and limit the intrinsic flexibility of graphene plasmons. Here, we demonstrate the visualization of plasmons in suspended graphene at room temperature, exhibiting high-quality factor Q~33 and long propagation length > 3 μm. We introduce the graphene suspension height as an effective plasmonic tuning knob that enables in situ change of the dielectric environment and substantially modulates the plasmon wavelength, propagation length, and group velocity. Such active control of micrometer plasmon propagation facilitates near-unity-order modulation of nanoscale energy flow that serves as a plasmonic switch with an on-off ratio above 14. The suspended graphene plasmons possess long propagation length, high tunability, and controllable energy transmission simultaneously, opening up broad horizons for application in nano-photonic devices.
  • Thumbnail Image
    Item
    Doping-driven topological polaritons in graphene/α-MoO3 heterostructures
    (Nature Publishing Group, 2022-09) Hu, Hai; Chen, Na; Teng, Hanchao; Yu, Renwen; Qu, Yunpeng; Sun, Jianzhe; Xue, Mengfei; Hu, Debo; Wu, Bin; Li, Chi; Chen, Jianing; Liu, Mengkun; Sun, Zhipei; Liu, Yunqi; Li, Peining; Fan, Shanhui; García de Abajo, F. Javier; Dai, Qing; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; National Center for Nanoscience and Technology Beijing; Barcelona Institute of Science and Technology; Peking University; CAS - Institute of Physics; Stony Brook University; Huazhong University of Science and Technology; Stanford University
    Control over charge carrier density provides an efficient way to trigger phase transitions and modulate the optoelectronic properties of materials. This approach can also be used to induce topological transitions in the optical response of photonic systems. Here we report a topological transition in the isofrequency dispersion contours of hybrid polaritons supported by a two-dimensional heterostructure consisting of graphene and α-phase molybdenum trioxide. By chemically changing the doping level of graphene, we observed that the topology of polariton isofrequency surfaces transforms from open to closed shapes as a result of doping-dependent polariton hybridization. Moreover, when the substrate was changed, the dispersion contour became dominated by flat profiles at the topological transition, thus supporting tunable diffractionless polariton propagation and providing local control over the optical contour topology. We achieved subwavelength focusing of polaritons down to 4.8% of the free-space light wavelength by using a 1.5-μm-wide silica substrate as an in-plane lens. Our findings could lead to on-chip applications in nanoimaging, optical sensing and manipulation of energy transfer at the nanoscale.
  • No Thumbnail Available
    Item
    Gate-tunable negative refraction of mid-infrared polaritons
    (American Association for the Advancement of Science, 2023-02-10) Hu, Hai; Chen, Na; Teng, Hanchao; Yu, Renwen; Xue, Mengfei; Chen, Ke; Xiao, Yuchuan; Qu, Yunpeng; Hu, Debo; Chen, Jianing; Sun, Zhipei; Li, Peining; de Abajo, F. Javier García; Dai, Qing; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; National Center for Nanoscience and Technology Beijing; Stanford University; CAS - Institute of Physics; Huazhong University of Science and Technology; ICFO - The Institute of Photonic Sciences
    Negative refraction provides a platform to manipulate mid-infrared and terahertz radiation for molecular sensing and thermal emission applications. However, its implementation based on metamaterials and plasmonic media presents challenges with optical losses, limited spatial confinement, and lack of active tunability in this spectral range. We demonstrate gate-tunable negative refraction at mid-infrared frequencies using hybrid topological polaritons in van der Waals heterostructures. Specifically, we visualize wide-angle negatively refracted polaritons in a-MoO 3 films partially decorated with graphene, undergoing reversible planar nanoscale focusing. Our atomically thick heterostructures weaken scattering losses at the interface while enabling an actively tunable transition of normal to negative refraction 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, enhanced molecular sensing, and on-chip optical circuitry.
  • No Thumbnail Available
    Item
    Tunable Planar Focusing Based on Hyperbolic Phonon Polaritons in alpha-MoO3
    (WILEY-V C H VERLAG GMBH, 2022-06-09) Qu, Yunpeng; Chen, Na; Teng, Hanchao; Hu, Hai; Sun, Jianzhe; Yu, Renwen; Hu, Debo; Xue, Mengfei; Li, Chi; Wu, Bin; Chen, Jianing; Sun, Zhipei; Liu, Mengkun; Liu, Yunqi; García de Abajo, F. Javier; Dai, Qing; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; National Center for Nanoscience and Technology Beijing; Peking University; Barcelona Institute of Science and Technology; University of Chinese Academy of Sciences; CAS - Institute of Physics; Stony Brook University
    Manipulation of the propagation and energy-transport characteristics of sub-wavelength infrared (IR) light fields is critical for the application of nanophotonic devices in photocatalysis, biosensing, and thermal management. In this context, metamaterials are useful composite materials, although traditional metal-based structures are constrained by their weak mid-IR response, while their associated capabilities for optical propagation and focusing are limited by the size of attainable artificial optical structures and the poor performance of the available active means of control. Herein, a tunable planar focusing device operating in the mid-IR region is reported by exploiting highly oriented in-plane hyperbolic phonon polaritons in alpha-MoO3. Specifically, an unprecedented change of effective focal length of polariton waves from 0.7 to 7.4 mu m is demonstrated by the following three different means of control: the dimension of the device, the employed light frequency, and engineering of phonon-plasmon hybridization. The high confinement characteristics of phonon polaritons in alpha-MoO3 permit the focal length and focal spot size to be reduced to 1/15 and 1/33 of the incident wavelength, respectively. In particular, the anisotropic phonon polaritons supported in alpha-MoO3 are combined with tunable surface-plasmon polaritons in graphene to realize in situ and dynamical control of the focusing performance, thus paving the way for phonon-polariton-based planar nanophotonic applications.