Research ArticleAPPLIED PHYSICS

Steering valley-polarized emission of monolayer MoS2 sandwiched in plasmonic antennas

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Science Advances  20 May 2020:
Vol. 6, no. 21, eaao0019
DOI: 10.1126/sciadv.aao0019
  • Fig. 1 Valley-controlled PL results of MoS2-antenna hybrid.

    (A) Representative examples (1012, 15, 16) of chiral metallic nanostructures to improve the light-matter interaction and steer the valley-polarized emission of TMDCs (blue balls). The performances were characterized by the DVP, footprint, and experimental temperature. The present stereoscopic antennas exhibited excellent chirality to form a valleytronics device with a small footprint and high DVP working at room temperature, as indicated by the red ball. (B) Schematic illustrations of a representative stereoscopic antenna with monolayer MoS2 sandwiched in the nanogap between two GNRs. (C) PL spectra for typical MoS2 monolayer (dots) and an LH antenna–MoS2 hybrid (lines) under circularly polarized excitation. a.u., arbitrary units. (D) Measured far-field PL patterns and corresponding normalized angular radiation distributions in polar coordinates for the bare MoS2 monolayer and the LH antenna–MoS2 hybrid.

  • Fig. 2 Directional emission measurements of monolayer MoS2 modified using the LH antenna with different intersection angles under σ+/σ− polarized excitation.

    (A) Schematic design of experimental setup using BFP imaging. (B) AFM scanning images and corresponding schematic diagrams for antennas with different configurations. (C and D) Experimental far-field PL patterns under σ+ (C)/σ− (D) polarized excitation and corresponding simulated far-field emission patterns obtained using the FDTD method.

  • Fig. 3 Simulations of the physical origin of far-field directional emission.

    (A) Scheme of calculation of far-field directional emission modified using the LH antenna. Top and bottom: top and side views of the structure, respectively. Yellow, GNRs. Blue, MoS2 monolayer. dA, diameter of GNR-A (85 nm); dB, diameter of GNR-B (60 nm); dg, the nanogap distance between GNRs (5 nm); d1 and d2, distances between the centerline of the GNRs and MoS2 (45 and 32.5 nm, respectively). (B) Schematic illustration of the dipole-dipole model. D1x and D1y represent the x/y components of the dipole pair’s moment, and D2 represents the induced dipole of the antenna. lx and ly represent the dipole-dipole separations between D1 and D2. (C and E) Simulated charge-density distributions in the X-Y plane. The dashed lines indicate the integrating regions for dipole moments D1 (gray) and D2 (black). (D and F) Analysis of the directivities of simulated far-field emission patterns with a σ− (D)/σ+ (F) dipole pair. Left: The far-field emissions calculated using the FDTD method. The simulated emission directivities were obtained by integrating the emission intensities over the two opposite intervals shown in the picture (black dotted lines). Right: Corresponding calculated results obtained using the dipole-dipole model.

  • Fig. 4 Valley-polarized PL measurements and FDTD simulations of LH antenna–MoS2 hybrid.

    (A and B) σ+ (red) and σ− (blue) polarized PL spectra of LH antenna–MoS2 hybrid under σ− (A) and σ+ (B) polarization excitation. (C) Electromagnetic field distribution under σ− and σ+ excitation at 633 nm at Z = 45 nm. (D) The antenna efficiency for the σ+ (red) and σ− (blue) dipole pairs as a function of wavelength. (E) Simulated EL and ER components at a wavelength of 675 nm in the near-field distribution under σ− polarization excitation. (F) Schematic illustrations of the modulation of valley exciton PL process using the LH antenna under σ− polarization excitation.

Supplementary Materials

  • Supplementary Materials

    Steering valley-polarized emission of monolayer MoS2 sandwiched in plasmonic antennas

    Te Wen, Weidong Zhang, Shuai Liu, Aiqin Hu, Jingyi Zhao, Yu Ye, Yang Chen, Cheng-Wei Qiu, Qihuang Gong, Guowei Lu

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