Temperature dependence of the Breit–Wigner–Fano Raman line in single-wall carbon nanotube bundles

The G band in Raman spectra of single-wall carbon nanotube (SWNT) bundles is studied between 3 and 500 K. The G band is best fit with five Lorentzian lines and one Breit–Wigner–Fano (BWF) line, indicating coupling of phonons to the electronic continuum of metallic SWNTs. It is found that the line width of the BWF line decreases with increasing temperature. This temperature-dependent behavior is contrary to that of the Lorentzian lines, where the line width increases with increasing temperature. The coupling constant 1/q of the BWF line is also found to decrease with increasing temperature. These temperature-dependent behaviors of BWF line provide evidence that it is the bundling effect of SWNTs that greatly enhances the BWF coupling.