Lattice vibrations of α′-NaV2O5

Lattice vibrations ofα′−NaV2O5Popova1, Sushkov2, Климин3 et al. 2002Phys. Rev. BSelf Cite215120View full textAdd to dashboardCite

“…The opening of a gap in the magnetic excitation spectrum below T c leads to a vanishing of a low-frequency continuum and to the appropriate transformation of the line shapes. Subsequent structure redetermination for the HT phase of α ′ -NaV 2 O 5 [2][3][4][5] does not, however, allow to ascribe E a polarized spectral continuum to a pure twospinon absorption. Symmetry considerations show that for both HT-and LT-structure of α ′ -NaV 2 O 5 the two-spinon (two-magnon) absorption is allowed only in E c polarization [33,34].…”

“…2c represents the spectra of a 150 µm thick sample). The a-polarized FIR absorption continuum extends to about 1500 cm −1 and consists of two bands centered at 300 and 1100 cm −1 [31,5,32]. Drastic changes occur in the spectra of NaV 2 O 5 at the transition temperature.…”

“…[5]); three strongly asymmetric phonon peaks at 90, 140, and 254 cm −1 visible on a strong absorption background in E a polarization; two strong phonon lines with ω T O = 163 and 180 cm −1 , ω LO = 169 and 215 cm −1 (compare with ω T O = 162 and 179 cm −1 , ω LO = 165 and 212 cm −1 as determined from FIR reflectance spectra at room temperature [5]) and an absorption peak at 282 cm −1 in E c polarization. This peak can be assigned to a missing B 1u phonon placed at 298 cm −1 by lattice dynamics calculations for the high-temperature (HT)-phase [5] and not observed in FIR reflectance spectra [5,26].…”

“…First of all, the calculated spectrum was fitted to the experimental one at T=37 K, just above the temperature of the phase transition, starting from the room temperature values determined earlier in our work [5]. The fitting to the low-temperature (T ≃10 K) spectrum was performed in two steps.…”

“…The model parameters were obtained in Ref. [5] by fitting to the HT-phase zone-center frequencies measured by optical techniques. In the present work, we use them to calculate the phonon dispersion curves throughout the Brillouin zone of the paraphase.…”