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Infrared hyperbolic metasurface based on nanostructured van der Waals materials

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Science  23 Feb 2018:
Vol. 359, Issue 6378, pp. 892-896
DOI: 10.1126/science.aaq1704
  • Fig. 1 Dipole-launching of hBN phonon polaritons.

    (A) Schematic of dipole launching of phonon polaritons on a 20-nm-thick hBN flake. h, height. (B) Simulated magnitude of the near-field distribution above the hBN flake, |E|. (C) Simulated real part of the near-field distribution above the hBN flake, Re(Ez). (D) Absolute value of the Fourier transform (FT) of panel (C). kx and ky are normalized to the photon wave vector k0. (E) Schematic of dipole launching of phonon polaritons on a 20-nm-thick hBN HMS (ribbon width w = 70 nm; gap width g = 30 nm). (F) Simulated magnitude of the near-field distribution above the hBN HMS, |E|. (G) Simulated real part of the near-field distribution above the hBN HMS, Re(Ez). (H) Absolute value of the FT of panel (G). The features revealed by the FT of the dipole-launched polaritons can be well fitted by a hyperbolic curve (white dashed lines). (I to L) Simulated magnitude of the near-field distributions for HMSs with different gap sizes and operation frequencies. The grating period w + g is fixed to 100 nm in all simulations. The white arrows in (B) and (F) display the simulated power flow.

  • Fig. 2 Polariton-interferometry imaging of phonon polaritons on a 20-nm-thick hBN HMS.

    (A) Schematic of the near-field polariton interferometry experiment. IR, infrared. (B) Topography image of the hBN HMS (nominal grating parameters are w ≈ 75 nm and g ≈ 25 nm; see also fig. S4). (C) Near-field images (amplitude signal s) recorded at four different frequencies. a.u., arbitrary units. (D) s-NSOM amplitude profiles along the solid (vertical) and dashed (horizontal) white lines in (C). (E) Illustration of the polariton interferometry contrast mechanism. The tip launches phonon polaritons on the HMS (indicated by simulated near fields). The polaritons with wave vector parallel to the grating reflect at the lower horizontal boundary (indicated by the black arrow) and interfere with the local field underneath the tip. Tip-launched polaritons propagating in other directions cannot be probed by the tip. The orange dashed lines mark the boundaries of the HMS. (F and G) Experimental (squares) and numerically calculated (solid lines) wave vectors of phonon polaritons on the unpatterned flake and the HMS, respectively. The line colors indicate the frequency ω according to (D).

  • Fig. 3 Wavefront imaging of antenna-launched HMS-PhPs.

    (A) Schematic of the experiment. (B) Topography image. The lines illustrate wavefronts of HMS-PhPs on the HMS (yellow and black) or phonon polaritons on the unpatterned flake (yellow and blue). (C) Near-field image recorded at ω = 1430 cm−1, clearly revealing concave wavefronts of HMS-PhPs emerging from the rod’s upper extremity.

  • Fig. 4 Frequency dependence of HMS-PhP wavefronts.

    (A and B) Experimental and calculated near-field distribution of HMS-PhPs launched by the antenna at three different frequencies. Black arrows in (A) indicate the fringes of polaritons launched by the tip and reflected at the boundary between the HMS and the unpatterned flake. Black dashed lines indicate the extremity of the gold rod. (C) Absolute value of the FT of the images shown in (A). White dashed lines represent the numerically calculated isofrequency curves of antenna-launched HMS-PhPs. The features in the gap between the hyperbolic isofrequency curves correspond to the FT of the antenna fields that are not coupled to polaritons (32), analogous to the central circular feature in the FT of the dipole-launched HMS-PhPs (Fig. 1H). The light-blue circle at ω = 1425 cm−1 marks a pixel whose value is still above the noise floor. The largest polariton wave vectors thus amount to about k = (kx2 + ky2)0.5 = [(15k0)2 + (15k0)2]0.5 > 20k0.

Supplementary Materials

  • Infrared hyperbolic metasurface based on nanostructured van der Waals materials

    Peining Li, Irene Dolado, Francisco Javier Alfaro-Mozaz, Fèlix Casanova, Luis E. Hueso, Song Liu, James H. Edgar, Alexey Y. Nikitin, Saül Vélez, Rainer Hillenbrand

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods 
    • Figs. S1 to S14 
    • References 

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