Lattice vibrations ofα′−NaV2O5

Abstract

We report high resolution polarized infrared studies of the quarter-filled spin ladder compound α ′ -NaV2O5 as a function of temperature (5 K≤ T ≤ 300 K). Numerous new modes were detected below the temperature Tc = 34 K of the phase transition into a charge ordered nonmagnetic state accompanied by a lattice dimerization. We analyse the Brillouin zone (BZ) folding due to lattice dimerization at Tc and show that some peculiarities of the low-temperature vibrational spectrum come from quadruplets folded from the BZ point ( ). We discuss an earlier interpretation of the 70, 107, and 133 cm −1 modes as magnetic bound states and propose the alternative interpretation as folded phonon modes strongly interacting with charge and spin excitations.

Low-energy excitations and dynamic Dzyaloshinskii-Moriya interaction inα′−NaV2ORõõm1, Hüvonen2, Nagel3 et al. 2004Phys. Rev. B261150View full textAdd to dashboardCite

“…6 and found by other groups 32,41 . The two low frequency modes, at 68 and 106 cm −1 , are the strongest.…”

“…Modes at frequencies close to 68 and 106 cm −1 have been found by Raman spectroscopy 42,43 . Sample dependence of mode frequencies by few wavenumbers has been observed both in infrared 32 and Raman 43 . It is known that Na deficiency of α ′ -Na x V 2 O 5 affects T c and in samples where x = 0.97 the phase transition is suppressed completely 44 .…”

Spin-gap mode in the charge-ordered phase ofNaV2O5studied by Raman scattering under high pressures

“…10-12͒ and far-infrared spectroscopy. 13,14 Meanwhile, a peak, which grows enough below T c and coincides approximately with the E g + spin-gap energy, was observed at about 64 cm −1 by Raman-scattering measurements. [15][16][17][18][19] Moreover, Konstantinović et al 20 found another peak at 86 cm −1 , which probably corresponds to the E g − magnetic excitation, by means of Raman scattering using the 647.1 nm light of Kr + -ion laser.…”

Zone-center phonons inNaV2O5: A comprehensiveab initiostudy including Raman spectra and electron-phonon interaction

“…11 In the lowtemperature phase, ions are displaced from their original positions by distances of the order of 0.05 Å. These displacements have been observed in x-ray diffraction [12][13][14][15][16][17] and can be estimated from infrared 18 and Raman spectroscopy. 19 They stabilize a phase containing zig-zag charge-ordering patterns.…”