Fig. 4.

Experimental spectra and theoretical simulations for the electron density dependence of the intersubband plasmon peak. a Optical absorption spectra showing how the ISBP peak evolves as the gate voltage increases. b Calculated single-particle absorption spectra for a (17, 0) semiconducting nanotube at different Fermi energy values. c Calculated single-particle absorption spectra for a metallic (10, 10) nanotube at different Fermi energy values. d Calculated perpendicular-polarization absorption spectra for a SWCNT with a diameter of 1.4 nm at different Fermi energy values based on a classical Drude plasmon model