title: Substrate phonon-mediated plasmon hybridization in coplanar graphene nanostructures for broadband plasmonic circuits.
abstract: The mode hybridization between adjacent graphene nanoribbons determines the integration density of graphene-based plasmonic devices. Here, plasmon hybridization in graphene nanostructures is demonstrated through the characterization of the coupling strength of plasmons in graphene nanoribbons as a function of charge density and inter-ribbon spacing using Fourier transform infrared microscopy. In combination with numerical simulations, it is shown that the plasmon coupling is strongly mediated by the substrate phonons. For polar substrates, the plasmon coupling strength is limited by the plasmon-phonon interactions. In contrast, a nonpolar substrate affects neither the energy distribution of the original plasmon modes in graphene nanostructures nor their plasmon interactions, which increases exponentially as the inter-ribbon spacing decreases. To further explore the potential of graphene broadband plasmonics on nonpolar substrates, a scheme is proposed that uses a metal-dielectric heterostructure to prevent the overlap of plasmons between neighboring graphene nanoribbons. The device structures retain the plasmon resonance frequency of the graphene ribbons and maximally isolate the plasmonic components from the surrounding electromagnetic environment, allowing modular design in integrated plasmonic circuits.
authors.affiliation: National Center for Nanoscience and Technology, Beijing, 100190, China.
authors.forename: Xiaoxia
authors.initials: X
authors.lastname: Yang
authors.forename: Xiang-Tian
authors.initials: XT
authors.lastname: Kong
authors.forename: Bing
authors.initials: B
authors.lastname: Bai
authors.forename: Zhenjun
authors.initials: Z
authors.lastname: Li
authors.forename: Hai
authors.initials: H
authors.lastname: Hu
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Qiu
authors.forename: Qing
authors.initials: Q
authors.lastname: Dai
keywords: electromagnetic coupling; graphene nanostructures; plasmonic circuits; substrate phonons; surface plasmons