Hertzian Fields and Tuning subdiffractional infrared polaritons in hexagonal Boron Nitride by engineered metasurface

The light-matter interaction in two-dimensional photonics crystals (2D-PC) occurs, primarily, via formation of polaritons, quasi-particules with subdiffractional wavelength originating of the coupling between photon and intrinsic vibrations of the materials, like phonons and plasmons.Weuse Synchrotron Infrared Nanospectroscopy (SINS) to study hyperbolic phonon polaritons (HP2) in2D-PCs crystals of hexagonal boron nitride (h-BN) lying on metallic (Au and Ag), dielectric (SiO2) substrates and on SiO2/Au metasurfaces. The HP2 modes are interpreted as Hertzian dipole waves, which behave differently depending on the substrate type. On metal, the wavelength of in-plane polarized HP2s is shortened, whereas, for out-of-plane polarized ones, the wavelength is enlarged. On the dielectrics, the oppositeis observed. We exploit this property, thus, in the metasurface by varying the thickness of the SiO2 layer to achieve wavelength tuning over more than 2 micrometers that is a record compared with tuning obtained with devices.