Stability of 1-D Excitons in Carbon Nanotubes under High Laser Excitations

TL;DR

This study demonstrates that interband exciton peaks in single-walled carbon nanotubes remain remarkably stable under high laser excitation, with spectral broadening explained by exciton interactions, challenging expectations of exciton dissociation at high densities.

Contribution

The paper provides experimental evidence of exciton stability in SWNTs under intense excitation, supported by theoretical estimates of exciton densities and Bohr radii, and explains spectral broadening phenomena.

Findings

Exciton peaks in SWNTs are stable under high laser excitation.

Presence of excitons causes broadening of absorption peaks.

Spectral dependence of pump-probe signals is explained by exciton interactions.

Abstract

Through ultrafast pump-probe spectroscopy with intense pump pulses and a wide continuum probe, we show that interband exciton peaks in single-walled carbon nanotubes (SWNTs) are extremely stable under high laser excitations. Estimates of the initial densities of excitons from the excitation conditions, combined with recent theoretical calculations of exciton Bohr radii for SWNTs, suggest that their positions do not change at all even near the Mott density. In addition, we found that the presence of lowest-subband excitons broadens all absorption peaks, including those in the second-subband range, which provides a consistent explanation for the complex spectral dependence of pump-probe signals reported for SWNTs.