X-Ray Anomalous Scattering Study of a Charge-Ordered State in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>NaV</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow><mml:mrow><mml:mn>5</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Nakao, Hironori; Ohwada, Kenji; Takesue, Naohisa; Fujii, Yasuhiko; Isobe, Masahiko; Ueda, Yutaka; Zimmermann, M. v.; Hill, J. P.; Gibbs, Doon; Woicik, J. C.; Koyama, Ichiro; Murakami, Youichi

doi:10.1103/physrevlett.85.4349

Cited by 73 publications

(43 citation statements)

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“…A quarter-filled ladder along the b-direction is formed, which explains one-dimensional magnetic properties of α ′ -NaV 2 O 5 above T c [2,8]. Below T c , a steep isotropic decrease of the magnetic susceptibility corresponding to a singlet-triplet gap of ∆=85 K [1,9] and a lattice dimerization described by the propagation wave vector k = [10] were recently found to be accompanied by a charge ordering of a zigzag type [7,[11][12][13] The nature of the state below T c is presently under intense investigation. The recent synchrotron X-ray diffraction studies of the low-temperature (LT) structure [6,14,15] resulted in the acentric space group F mm2-C 18 2v with three essentially different positions for the vanadium atoms arranged into a sequence of zigzag modulated ladders separated by nonmodulated ones (see Fig.…”

Section: Introductionmentioning

confidence: 99%

“…More recent bond-valence calculations suggest, however, only two vanadium valences despite the three crystallographically inequivalent V sites [15]. Nevertheless, several observations, in particular, the properties of X-ray anomalous scattering [13], can be better explained if one assumes the modulation of all the vanadium ladders, and therefore different subgroups of F mm2 were considered [17,18]. In their Raman scattering study of folded modes, the authors of Ref.…”

Section: Introductionmentioning

confidence: 99%

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Lattice vibrations ofα′−NaV2O5
Popova
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Sushkov
²
,
Климин
³

et al. 2002
Phys. Rev. B
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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.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Lattice vibrations ofα′−NaV2O5
Popova
¹
,
Sushkov
²
,
Климин
³

et al. 2002
Phys. Rev. B
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“…2,4 -8 The first interpretation of this phenomenon was related to a model of different V 4ϩ and V 5ϩ chains and associated with the spin-Peierls transition in V 4ϩ chains. 1 However, recent experiments 7,8 show that above T c all vanadium ions are equivalent (V 4.5ϩ ), whereas below T c , a charge disproportionation appears. Analysis of the additional experimental data on the microwave dielectric susceptibility, entropy change at T c , and magnetic-field effect on T c has led to an unambigious conclusion about zigzag charge ordering ͑for a review, see Ref.…”

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confidence: 99%

“…[1][2][3][4][5][6][7][8][9][10][11][12] It exhibits a remarkable phase transition at T c ϭ34 K, now identified as chargeordering of the zigzag type. 2,4 -8 The first interpretation of this phenomenon was related to a model of different V 4ϩ and V 5ϩ chains and associated with the spin-Peierls transition in V 4ϩ chains.…”

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Nature of insulating state inNaV2O5above charge-ordering transition: A cluster dynamical mean-field study

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The nature of the insulating state driven by electronic correlations in the quarter-filled ladder compound ␣ЈNaV 2 O 5 is investigated within a cluster dynamical mean-field approach. An extended Hubbard model with first-principles tight-binding parameters has been used. It is shown that the insulating state in the chargedisordered phase of this compound is formed due to the transfer of spectral density and dynamical charge fluctuations where for the latter, the role of intersite Coulomb interaction is found to be of crucial importance. (V 4.5ϩ ), whereas below T c , a charge disproportionation appears. Analysis of the additional experimental data on the microwave dielectric susceptibility, entropy change at T c , and magnetic-field effect on T c has led to an unambigious conclusion about zigzag charge ordering ͑for a review, see Ref. 9͒.Both the charge-ordered phase and charge-disordered one are insulating with an energy gap of the order of 0.8-1 eV. 3The presence of the gap in the ordered phase is not surprising and it was reproduced successfully, for example, in the recent local-density approximation ͑LDA͒ϩU calculations. 11The properties of the disordered phase are much more difficult to understand. In contrast to the isostructural ladder compound CaV 2 O 5 , NaV 2 O 5 has a quarter-filled band 2 rather than a half-filled one and cannot be considered as a standard Mott insulator. It has been proposed in Refs. 5 and 6 that a large value of the transverse hopping parameter in the ladder which splits the band into sub-bands of the bonding and antibonding states 2 could be responsible for the Mott insulator behavior in NaV 2 O 5 in the presence of strong Coulomb interactions. However, it is not known whether this mechanism is adequate for the realistic values of the parameters characterizing the single-particle electronic structure and the electron-electron correlations.In this paper we investigate the correlation effects in NaV 2 O 5 taking into account nonlocal dynamical charge fluctuations on the rung for this two-leg ladder compound. This allows us to understand the origin of the insulating state above T c and to estimate the relative importance of various physical mechanisms responsible for the gap formation.The crystal structure of NaV 2 O 5 projected in the xy plane is sketched in Fig. 1 Fig. 1͒. In this state one has approximately one d electron per rung of the vanadium ladder. We start with LDAϩU ͑Ref. 13͒ calculations of the ordered states but, in contrast to the previous work, 11 we considered several different types of the charge ordering. This gives us an opportunity to estimate the on-site and intersite Coulomb interactions U and V.It is natural to assume that the tendency to keep the number of d electrons per rung close to unity also takes place above the transition temperature leading to strong shortrange order and well-developed dynamical charge fluctuations. This is confirmed by the temperature dependencies of the spin gap and the entropy measurements.12 Usual LDA as well as the mean-field th...

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“…Various experiments, including anomalous X-ray scattering [17], inelastic neutron scattering [18], Raman spectroscopy [19], and NMR [20,21], have suggested zigzag charge order on all ladders. Such a model is at variance with the published crystal structure, and it is not possible for any ordered structure with Fmm2 symmetry [8].…”

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confidence: 99%

Orthorhombic versus monoclinic symmetry of the charge-ordered state ofNaV2O5

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High-resolution X-ray diffraction data show that the lowtemperature superstructure of α ′ -NaV2O5 has an F −centered orthorhombic 2a × 2b × 4c superlattice. A structure model is proposed, that is characterized by layers with zigzag charge order on all ladders and stacking disorder, such that the averaged structure has space group Fmm2. This model is in accordance with both X-ray scattering and NMR data. Variations in the stacking order and disorder offer an explanation for the recently observed devils staircase of the superlattice period along c. 61.50. Ks; 61.44.Fw; 61.66.Fn; 75.30.Fv The low dimensional transition metal oxide α ′ -NaV 2 O 5 undergoes a phase transition at a temperature of T c = 34 K. The transition is characterized by the development of both a nonmagnetic groundstate and a superstructure [1,2]. General agreement exists that the phase transition is associated with the development of charge order on the vanadium sublattice [3,4], but the mechanism of the transition has not been revealed yet.At room temperature α ′ -NaV 2 O 5 crystallizes in space group Pmmn [5][6][7]. There is one crystallographically independent vanadium atom, that is in the mixed-valence state 4.5+. The structure can be considered as built of layers of two-leg ladders V 2 O 3 , that are stacked along c, alternating with sodium atoms and additional oxygen. The lattice parameters of the basic structure at 15 K are a = 11.294Å, b = 3.604Å, and c = 4.755Å [8]. The superlattice below T c can be described by an F −centered orthorhombic 2a × 2b × 4c supercell. The superstructure was found to have symmetry F mm2, but it showed two peculiar features [8,9]: (i) In one layer ladders with zigzag charge order alternate with ladders with vanadium in the mixed-valence state, (ii) Each of the two consecutive layers contains half of the six crystallographically independent vanadium atoms, but their structures were nearly equal. This crystal structure was found to be in agreement with two other X-ray diffraction measurements [10,11].Theoretical analyses have produced models that show zigzag charge order on all ladders [3,4,[12][13][14][15][16]. However, most approaches did not consider the true supercell, and therefore they cannot be expected to reveal all aspects of the mechanism of the phase transition.Various experiments, including anomalous X-ray scat- In order to determine the true superstructure of NaV 2 O 5 , we have measured high-resolution, highsensitive synchrotron radiation X-ray diffraction. The experiment indicates that the true superlattice is F −centered on the 2a × 2b × 4c supercell. We show that an all zigzag charge order model with orthorhombic symmetry is possible assuming stacking disorder. This model is in agreement with both X-ray diffraction and NMR.X-ray diffraction experiments were performed at beamline ID10A of the ESRF in Grenoble, France. Monochromatic radiation of a wavelength of λ = 0.66057Å was selected by the 220 reflection of diamond. Bragg reflections were measured by ω−scans using a scintillation detector.N...

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X-Ray Anomalous Scattering Study of a Charge-Ordered State inNaV2O5

Cited by 73 publications

References 24 publications

Lattice vibrations ofα′−NaV2O5
Popova
¹
,
Sushkov
²
,
Климин
³

et al. 2002
Phys. Rev. B
Self Cite
21
5
12
0
View full text Add to dashboard Cite

Lattice vibrations ofα′−NaV2O5
Popova
¹
,
Sushkov
²
,
Климин
³

et al. 2002
Phys. Rev. B
Self Cite
21
5
12
0
View full text Add to dashboard Cite

Nature of insulating state inNaV2O5above charge-ordering transition: A cluster dynamical mean-field study

Orthorhombic versus monoclinic symmetry of the charge-ordered state ofNaV2O5

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X-Ray Anomalous Scattering Study of a Charge-Ordered State inNaV2O5

Cited by 73 publications

References 24 publications

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

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

Nature of insulating state inNaV2O5above charge-ordering transition: A cluster dynamical mean-field study

Orthorhombic versus monoclinic symmetry of the charge-ordered state ofNaV2O5

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Lattice vibrations ofα′−NaV2O5
Popova
¹
,
Sushkov
²
,
Климин
³

et al. 2002
Phys. Rev. B
Self Cite
21
5
12
0
View full text Add to dashboard Cite

Lattice vibrations ofα′−NaV2O5
Popova
¹
,
Sushkov
²
,
Климин
³

et al. 2002
Phys. Rev. B
Self Cite
21
5
12
0
View full text Add to dashboard Cite