Fig. 3
Mode characteristics and evolution with wavelengths (λ) of the PEPP. a Mode profiles in terms of energy density distributions, showing the mode transition between SPP-like and exciton-like characters, (i–v) λ = 560, 596, 616, 636, and 680 nm, respectively. b Quantitative characterization in terms of fractional energy inside the MNW (ηm) and the WS2 layer (ηl). ηm and ηl for PEPP (SPP) are denoted by squared red and dot blue lines (red and blue dashed lines), respectively. For the SPP, ηl is calculated by setting oscillator strength of the WS2 cladding to be zero. For the PEPP, black dashed line indicates ηl = 0.5, and blue-filling area indicates the exciton-like region. Green circles: ηm for PEPPs at the wavelengths of 560, 596, 616, 636, and 680 nm shown in a. Their corresponding ηm are ~ 0.46 a(i), ~ 0.32 a(ii), ~ 0.03 a(iii), ~ 0.32 a(iv), and ~ 0.40 a(v), respectively. c Normalized energy density along x direction W(x, 0) at λ = 616 nm. Yellow line: PEPP. Gray solid and dashed lines: SPP and its 10 times multiplication for clear visualization. Inset: coordinates on the cross section. The diameter for the Ag MNW here is 50 nm