Fig. 3: Evolution of the dispersive polaritons at ERP1 in monoclinic crystal Y2SiO5.
a–d the measured near-field signal |S2| with different incident frequencies using s-SNOM. The PhPs are launched by an Au nanodisk antenna with a diameter of ~1 μm and thickness of 100 nm. The incident laser beam is aligned with the x-axis with p-polarization. e–h corresponding Fourier spectrum of the panel (a–d) obtained by calculating their Fourier transformation. i–l the Fourier spectrum of dipole-launched polaritons through numerical simulations. The z-oriented dipole is placed 100 nm above the crystal surface. The green arrows indicate the TA at different frequencies, which is moving far away from OB with increasing frequency. White curves indicate the iso-intensity contours (the points on the curve have the same intensity of the mode distribution) and the unequal lengths (the length between the original point and the furthest point of the iso-intensity contour of each petal) of the neighboring branches present the unbalanced shear response in the LSC. m the evolution of θ and n open angle γ versus frequency near ERP1. As indicated in the inset, θ is defined as the angle between TA and the x-axis. The values of θ and γ both have a 90-degree step change at ERP1. Blue solid curve: calculated theoretical results by tan−1[-Re(ε2)/Re(ε1)]; red dots: simulation results obtained from the dipole launched polaritons using the finite-element method same as panel (i–l) (see “Methods”); yellow pentacles: experimental results obtained by measuring the near-field optical signals under the excitations of different frequencies using s-SNOM (see “Methods”). Inset in panel (m) the analytically calculated imaginary part of the reflection coefficient at 920 cm−1.
