RESONANT RAMAN-SCATTERING AND THE ZONE-FOLDED ELECTRONIC-STRUCTURE INSINGLE-WALL NANOTUBES

Resonant Raman scattering from optical phonons in single-wall nanotube s of mean diameter 1.1 nm has been measured for incident laser beams w ith wavelength between 450 and 800 nm. The scattering intensities exhi bit anomalies in the vicinity of 690 nm, there being a minimum in the longitudinal components and a maximum in the transverse. Our optical-t ransmission measurement also exhibits a dip in the same photon energy range. The anomalies are caused by the incident laser beam resonant wi th the zone-folded electronic structures in nanotubes. These results p rovide direct experimental evidence of the critical point in the densi ty of states produced by the cylindrical symmetry of nanotubes.