The tangential G-band in the Raman spectra of a metallic single-wall carbon nanotube shows two peaks: a higher frequency component having the Lorentzian shape and a lower-frequency component of lower intensity with a Breit-Wigner-Fano (BWF)-type lineshape. This interesting feature has been analyzed on the basis of phonon-plasmon coupling in a nanotube. It is shown that the low-lying optical plasmon corresponding to the tangential motion of the electrons on the nanotube surface can explain the observed features. In particular, this theory can explain occurrence of both the Lorentzian and BWF lineshapes in the G-band Raman spectra of metallic single-wall carbon nanotubes. Furthermore, the theory shows that the BWF peak moves to higher frequency, has a lower intensity and a lower half width at higher diameters of the nanotube. All these features are in agreement with experimental observations. 2
The coupling of photons with long-wavelength magnons in antiferromagnetic MnF, in the presence of an externally applied magnetic field in the body c direction is investigated. It is found that two pure, circularly polarized modes can propagate in the crystal along the direction of the magnetic field. A study of the reflection spectra for normally incident plane-polarized radiation reveals that an antiferromagnetic crystal in an applied magnetic field can be used as an optical device to obtain pure, circularly polarized radiation.
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