Search

Excitonic effects in 1D semiconductors can be qualitatively different from those in higher dimensions. In particular, the Sommerfeld factor, the ratio of the above-band-edge excitonic continuum absorption to free electron-hole pair generation, has been shown to be less than 1 (suppressed) in 1D systems while it is larger than 1 (enhanced) in 2D and 3D systems. Strong continuum suppression indeed exists in semiconducting single-wall carbon nanotubes, a prototypical 1D semiconductor. However, absorption spectra for carbon nanotubes are typically fit with a combination of Lorentzians and a polynomial background baseline with little physical meaning. Here, we performed absorption measurements in aligned single-chirality (6,5) carbon nanotube films. The obtained spectra were fit with our theoretical model obtained by solving the Boltzmann scattering equation involving fifty-nine different types of transitions among three different types of quasiparticles. Specifically, we took into account microscopic interactions between photons, phonons, and excitons, including their dispersions, which unambiguously demonstrated that the background absorption is due to phonon-assisted transitions from the semiconductor vacuum to finite-momentum continuum states of excitons. The excellent agreement we obtained between experiment and theory suggests that our numerical technique can be seamlessly extended to compute strongly out-of-equilibrium many-body dynamics and time-resolved spectra in low-dimensional materials. [Display omitted] [ABSTRACT FROM AUTHOR]

The exciton states in the single-walled carbon nanotubes (SWNTs) with Stone–Wales (SW) defects are theoretically studied in the tight-binding model. It is found that for the semiconducting zigzag tubes (10, 0) with different concentration of SW defect, the exciton energies move to low energy region with increasing the concentration of SW defect, and the symmetry broken by the SW defects leads to splitting of the degenerate exciton energy levels, which can be seen clearly from the linear absorption spectra of defected SWNTs. As detected from the linear absorption spectra, we can give some information on the concentration of the SW defect existing in the SWNTs. [ABSTRACT FROM AUTHOR]