Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMagnetic Resonance in the Spin-Peierls compound $alpha-NaV_2O_5$
104
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present results from magnetic resonance measurements for 75-350 GHz in $alpha$-NaV$_{2}$O$_{5}$. The temperature dependence of the integrated intensity indicates that we observe transitions in the excited state. A quantitative description gives resonances in the triplet state at high symmetry points of the excitation spectrum of this Spin-Peierls compound. This energy has the same temperature dependence as the Spin-Peierls gap. Similarities and differences with the other inorganic compound CuGeO$_{3}$ are discussed.
rate research
Read More
Infrared reflectance of alpha-NaV2O5 single crystals in the frequency range from 50 cm-1 to 10000 cm-1 was studied for a, b and c-polarisations. In addition to phonon modes identification, for the a-polarised spectrum a broad continuum absorption in the range of 1D magnetic excitation energies was found. The strong near-IR absorption band at 0.8 eV shows a strong anisotropy with vanishing intensity in c-polarisation. Activation of new phonons due to the lattice dimerisation were detected below 35K as well as pretransitional structural fluctuations up to 65K.
At room-temperature NaV2O5 was found to have the centrosymmetric space group Pmmn. This space group implies the presence of only one kind of V site in contrast with previous reports of the non-centrosymmetric counterpart P21mn. This indicates a non-integer valence state of vanadium. Furthermore, this symmetry has consequences for the interpretation of the transition at 34 K, which was ascribed to a spin-Peierls transition of one dimensional chains of V4+.
Polarized far-infrared (FIR) spectroscopic measurements and FIR magneto-optical studies were performed on the inorganic spin-Peierls compound CuGeO_3. An absorption line, which was found at 98 cm$^{-1}$ in the dimerized phase (D phase), was assigned to a folded phonon mode of B$_{3u}$ symmetry. The splitting of the folded mode into two components in the incommensurate phase (IC phase) has been observed for the first time. A new broad absorption centered at 63 cm$^{-1}$ was observed only in the ${bf E}parallel b$ axis polarization, which was assigned to a magnetic excitation from singlet ground state to a continuum state.
We argue that in the quarter-filled ladder compound NaV_2O_5 the quasi-one-dimensional spin system is strongly coupled to a low-energy antiferroelectric mode of the excitonic type. This mode results from the interplay between the electron hopping along the rungs of the vanadium two-leg ladders and the Coulomb repulsion between electrons. The charge ordering observed in sodium vanadate at T_c = 34K corresponds to the softening of the antiferroelectric mode. We consider the spin-isospin model, which describes the spin and low-energy charge degrees of freedom in sodium vanadate. Within this model we explain the observed anomalous temperature-dependence of the dielectric susceptibility at T_c and the midinfrared absorption continuum. We identify the broad structure in the low-energy optical absorption spectrum of NaV_2O_5 with the continuum formed by two spinons and one low-energy charge excitation.
We present a detailed analysis of light scattering experiments performed on the quarter-filled spin ladder compound $alpha^prime$-NaV$_{2}$O$_{5}$ for the temperature range 5 K$le$T$le$300 K. This system undergoes a phase transition into a singlet ground state at T=34 K accompanied by the formation of a super structure. For T$leq$34 K several new modes were detected. Three of these modes are identified as magnetic bound states. Experimental evidence for charge ordering on the V sites is detected as an anomalous shift and splitting of a V-O vibration at 422 cm$^{-1}$ for temperatures above 34 K. The smooth and crossover-like onset of this ordering at T$_{rm CO}$= 80 K is accompanied by pretransitional fluctuations both in magnetic and phononic Raman scattering. It resembles the effect of stripe order on the super structure intensities in La$_2$NiO$_{4+delta}$.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
