Resonant Raman scattering in NaV2O5 as a probe of its electronic structure

Details Resonant Raman scattering in NaV2O5 as a probe of its electronic structure Resonant Raman scattering in NaV2O5 as a probe of its electronic structure

1999-07-16

arxiv.org/abs/cond-mat/9907237v1

phys. stat. sol. (b) 215, 661 (1999).

Physics

Condensed Matter

Strongly Correlated Electrons

to be publish in physica status solidi (proceedings issue of ICSSS)

Scientific paper

In order to investigate the origin of the phase transition observed in NaV$_2$O$_5$, as well as its electronic structure, we have measured Raman intensities as a function of the laser wavelength above and below the phase transition temperature. In the polarized Raman spectra at room temperature we observe resonant enhancement of the 969 $cm^{-1}$ phonon mode when the laser energy approaches 2.7 eV, presumably related to the (p-d) electron hopping band, $O_3$($p_y$)-V($d_{xy}$), at 3.2 eV. The 969 $cm^{-1}$ mode originates from the stretching vibrations along the c-axis involving the V-$O_1$ bonds. Since an ellipsometric determination of the dielectric function $\epsilon_{cc}$ yields no structure in the 1.7 to 5.5 eV photon energy range, we conclude that plane bonds couple strongly with the apical oxygens leading to a large Raman efficiency. In the low-temperature Raman spectra, almost all modes that become active below the phase transition temperature T$_c$=34 K show resonant behavior. The most interesting ones, those at 66 and 106 $cm^{-1}$, possibly of magnetic origin, exhibit a resonant intensity enhancement, approximately by an order of magnitude, for laser photon energies around 1.85 eV with respect to 2.43 eV. This resonance effect may be associated with a weak absorption band around 2 eV. Finally, a destructive interference between the resonant and the nonresonant contribution to the Raman scattering amplitude (i.e. an antiresonance) is found in the spectra for most of the (bb) low-temperature modes.

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