Anisotropic Flow Control and Gate Modulation of Hybrid Phonon-Polaritons

摘要： Light-matter interaction in two-dimensional photonic materials allows for confinement and manipulation of free-space radiation in sub-wavelength scales. Most notably, the van der Waals heterostructure comprising graphene (G) and hexagonal Boron Nitride (hBN) provides for gate-tunable hybrid hyperbolic plasmon phonon-polaritons (HP3). Here, we present anisotropic flow control and gate voltage modulation of HP3 modes in G-hBN lying on air-Au microstructured substrate. Using broadband infrared synchrotron radiation coupled to a scattering-type near-field optical microscope, we launch HP3 waves in both hBN Reststrahlen bands and observe directional propagation across in-plane heterointerfaces created at the air-Au junction. HP3 hybridization is modulated by varying the gate voltage between graphene and Au. In this case, we induce modifications to the coupling of continuum graphene plasmons with the discrete hBN hyperbolic phonon polaritons, which is interpreted as an extended Fano model. This is the first demonstration of control of polariton propagation, including a theoretical approach for a break of the reflection/transmission symmetry for HP3 modes. Our findings augment the degree of control of polaritons in G-hBN and related hyperbolic metamaterial nanostructures bringing novel insights to on-chip nano-optics communication and computing.