  Hyperbolic metasurfaces based on van der Waals (vdW) materials support
propagation of extremely anisotropic polaritons towards nanoscale light
compression and manipulation, and thus has great potential in the applications
of planar hyperlens, nanolasing, quantum optics and ultrasensitive infrared
spectroscopy. Two-dimensional hexagonal boron nitride (h-BN) as a vdW
metasurface can manipulate the propagation of hyperbolic polaritons at the
level of single atomic layers, possessing higher degree of field confinement
and lower losses than the conventional media. However, active manipulation of
hyperbolic polaritonic waves in h-BN midinfrared metasurfaces remains elusive.
Herein, we provide an effective strategy for constructing tunable mid-infrared
hyperbolic vdW metasurfaces (HMSs). They are composed of meta-atoms that are
the in-plane heterostructures of thin-layer h-BN and monolayer graphene strips
(iHBNG). The strong coupling of h-BN phonons and graphene plasmons enables the
large tunability of light fields by tailoring chemical potentials of graphene
without frequency shift, which involves topological transitions of polaritonic
modes, unidirectional polariton propagation and local-density-of-state
enhancement. Simulated visual near-field distributions of iHBNG metasurfaces
reveal the unique transformations of hyperbolic polariton propagations,
distinguished from that of individual h-BN and graphene metasurfaces. Our
findings provide a platform of optical nanomanipulation towards emerging
on-chip polaritonic devices.
