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.
Bibliographical noteFunding Information:
The authors acknowledge Dr. Zhiyuan Sun (Department of Physics, Columbia University) for valuable discussions and acknowledge Nanofab Lab @ NCNST for helping with sample fabrication. This work was supported by the National Key Research and Development Program of China (Grant No. 2020YFB2205701), the National Natural Science Foundation of China (Grant Nos. 51902065, 52172139, 51925203, U2032206, 52072083, and 51972072), Beijing Municipal Natural Science Foundation (Grant No. 2202062), and Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB36000000, XDB30000000). F.J.G.A. acknowledges the ERC (Advanced Grant 789104- eNANO), the Spanish MINECO (PID2020-112625GB-I00 and SEV2015-0522), and the CAS President’s International Fellowship Initiative (PIFI) for 2021. Z.P.S. acknowledges the Academy of Finland (Grant Nos. 314810, 333982, 336144 and 336818), The Business Finland (ALDEL), the Academy of Finland Flagship Programme (320167,PREIN), the European Union’s Horizon 2020 research and innovation program (820423,S2QUIP; 965124, FEMTOCHIP), the EU H2020-MSCA-RISE-872049 (IPN-Bio), and the ERC (834742). P.A.-G. acknowledges support from the European Research Council under Starting Grant No. 715496, 2DNANOPTICA, and the Spanish Ministry of Science and Innovation (Grant Number PID2019-111156GB-I00).
© 2022, The Author(s).