Low-energy excitations and dynamic Dzyaloshinskii-Moriya interaction inα′−NaV2O

Abstract

We have studied far infrared transmission spectra of α ′ -NaV2O5 between 3 and 200 cm −1 in polarizations of incident light parallel to a, b, and c crystallographic axes in magnetic fields up to 33 T. The temperature dependence of the transmission spectra was studied close to and below the phase transition temperature Tc = 34 K. The triplet origin of an excitation at 65.4 cm −1 (8.13 meV) is revealed by splitting in the magnetic field. The g-factors for the triplet state are ga = 1.96 ± 0.02, g b = 1.975 ± 0.004 and gc = 1.90 ± 0.03. The magnitude of the spin gap at low temperatures is found to be magnetic field independent at least up to 33 T. All other infrared-active transitions appearing below Tc are ascribed to zone-folded phonons. Two different dynamic DzyaloshinskiiMoriya (DM) mechanisms have been discovered that contribute to the oscillator strength of the otherwise forbidden singlet to triplet transition. First, the strongest singlet to triplet transition is an electric dipole transition where the polarization of the incident light's electric field is parallel to the ladder rungs (E1 a). This electric dipole active transition is allowed by the dynamic DM interaction created by a high frequency optical a-axis phonon. Second, in the incident light polarization perpendicular to the ladder planes (E1 c) an enhancement of the singlet to triplet transition is observed when the applied magnetic field shifts the singlet to triplet resonance frequency to match the 68 cm −1 c-axis phonon energy. The origin of the second mechanism is the dynamic DM interaction created by the 68 cm −1 c-axis optical phonon. The strength of the dynamic DM is calculated for both mechanisms using the presented theory.

Microscopic mechanisms of spin-dependent electric polarization in3doxides

“…It is easy to see that this quantity has a clear physical meaning to be in fact a dipole matrix element for a singlettriplet electrodipole transition in our three-site cluster. [54][55][56] First of all we should take into account the singlet-triplet mixing effects for the ground-state manifold, which are governed by Dzyaloshinsky-Moriya interactions,…”

Magnetic excitations and optical transitions in the multiferroic spin-12systemLiCu2OHüvonen1, Nagel2, Rõõm3 et al. 2009Phys. Rev. BSelf Cite283200View full textAdd to dashboardCite

“…Terahertz absorption spectra were recorded using a MartinPuplett spectrometer with a 0.3 K bolometer and a rotatable polarizer in front of the sample. 24 Several strong phonon absorption lines are seen in the absolute spectra in Fig. 2.…”

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.…”

“…11 and 12͒ and by farinfrared spectroscopy. 14 The damping constant ⌫ is almost independent of temperature. Figure 5 shows the T-P phase diagram, which was determined below 2 GPa by means of x-ray diffraction.…”