Fig. 3: SINS spectra on a SrTiO3 membrane supported by gold- and SiO2.
From: Highly confined epsilon-near-zero and surface phonon polaritons in SrTiO3 membranes
a, c Symbols: SINS second-harmonics amplitude spectra (“sam”) of the membrane on gold- (a) and on SiO2/Si (c) normalized to the signal from bare gold (“ref”). Solid lines: finite-dipole model based on the dielectric function of bulk SrTiO3. b,d Calculated imaginary part of the complex reflection coefficient \({r}_{p}(q,\omega )\) for the 100 nm SrTiO3 membrane on gold and on SiO2/Si, respectively. Dashed-dotted Vertical lines in (a–d) denote the LO and TO frequencies of bulk SrTiO3. “sym" and “asym” refer to symmetric and antisymmetric modes, respectively. Green crosses in Fig.3d represent the data points in Fig.4g. e Schematic describing the SINS spectra acquisition. f–i Simulated distribution of the electromagnetic field, when the sample is illuminated with a plane wave and a gold nanobeam (marked with a black rectangle) is placed on top in order to excite waves with finite in-plane momenta, for the membrane on gold at 787 and 560 cm−1, respectively (e, f), and for the membrane on SiO2/Si at the same frequencies (marked with dashed lines in (a–d)). h, i In gold, the electromagnetic field is negligibly small.
