Anisotropic optical spectra in a detwinned<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">LaMnO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>crystal

Tobe, K.; Kimura, T.; Okimoto, Y.; Tokura, Y.

doi:10.1103/physrevb.64.184421

Cited by 98 publications

(92 citation statements)

References 27 publications

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“…Based on the above analysis, we expect that only the yz ± zx DOS will cross E F as T is increased above T MI , while the xy DOS will still show insulating behavior. A detailed analysis of the anisotropic optical spectra across the MI transition driven by strong changes in orbital occupation can also verify the proposed scenario [15].…”

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confidence: 86%

VO ₂ : A two-fluid incoherent metal?

2005

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We present ab initio LDA+DMFT results for the many-particle density of states of V O2 on the metallic side of the strongly first-order (T -driven) insulator-metal transition. In strong contrast to LDA predictions, there is no remnant of even correlated Fermi liquid behavior in the correlated metal. Excellent quantitative agreement with published photoemission and X-ray absorption experiments is found in the metallic phase. We argue that the absence of FL-quasiparticles provides a natural explanation for the bad-metallic transport for T > 340 K. Based on this agreement, we propose that the I-M transition in V O2 is an orbital-selective Mott transition, and point out the relevance of orbital resolved one-electron and optical spectroscopy to resolve this outstanding issue. A detailed understanding of the above cases is still somewhat elusive. In particular, it is still unclear whether the MIT is orbital selective, i.e., whether different orbital-resolved densities-of-states (DOS) are gapped (driving the Mott insulating state) at different values of U, U ′ (defined below) or whether there is a single (common) Mott transition at a critical interaction strength [3,4]. Conflicting results, even for the same system, and within the same (d = ∞) approximation [4] have been obtained, necessitating more work to resolve this issue.In this communication, we address precisely this issue in vanadium dioxide (V O 2 ). Using the state-of-the-art LDA+DMFT [5] technique, we first show how excellent quantitative agreement with the full, local one-electron spectral function is achieved using LDA+DMFT(IPT). We then build on this agreement, claiming that the MIT in V O 2 is orbital selective, and represents a concrete, ab initio realization of the two-fluid scenario for MIT in strongly correlated systems.V O 2 shows a spectacular MIT at T = 340 K from a low-T monoclinic, Mott insulating phase with spin dimerization along the crystallographic c-axis to a local moment paramagnetic metallic phase. This T -driven MIT has attracted intense scrutiny: because of the additional complication of the antiferroelectric displacement of the V O 6 octahedra in a correlated system, an unambiguous characterization of the MIT (relative importance of MottHubbard versus Peierls dimerization) is somewhat difficult. Various observations have been cited in support of both scenarios [1], and theoretical models detailing the importance of these effects have been proposed [6,7].One-electron spectroscopies constitute a reliable fingerprint of the changes in the single-particle spectral

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confidence: 86%

VO ₂ : A two-fluid incoherent metal?

2005

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“…Experimentally manganites are not very far from the metallic state. Although being insulating, undoped LaMnO 3 has relatively small energy gap, by optical data of the order of 0.4 eV [5]. Moreover the conductivity of RMnO 3 considerably increases above the temperature of the orbital ordering [7].…”

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confidence: 99%

Orbital ordering in manganites in the band approach

Efremov¹,

Khomskii²

2005

Phys. Rev. B

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We consider the orbital ordering in LaMnO3 and similar systems, proceeding from the band picture. We show that for the realistic magnetic structure of A-type there exists a complete nesting betweeen two eg-bands. As a result there occurs an instability towards an excitonic insulator-like state -an electron-hole pairing with the wave vector Q = (π, π), which opens a gap in the spectrum and makes the system insulating. In the resulting state there appeasr an orbital ordering -orbital density wave (ODW), the type of which coincides with those existing in LaMnO3.

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“…The solid line is a fit of the RXS intensity as described in the text. Inset: Θ-dependence of the normalized optical spectral weight Ic/I ab following [21] (solid line) with the experimentally derived Θ-values; (b) T -dependence of c1 and c2 determined by ND taken from [5]. The dashed lines were obtained using…”

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“…3(a)) between the optical spectral weight with the polarization within the ferromagnetic (FM) plane (there ab) and along the AFM axis (there c). [21] Their simple model suggests a value Θ∼74 • to describe the experimental value of I c /I ab =0.6 at 10 K in the AFM regime. Theoretically, only a slight decrease of Θ below T N is expected [7,22] and therefore above T N Θ ESR ∼92 • yields a better description of the anisotropic properties of LaMnO 3 in the orbitally ordered state than Θ ND ∼106 • .…”

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Orbital order parameter inLa0.95Sr0.05MnO3

Kochelaev¹,

Shilova²,

Balbashov³

et al. 2003

Phys. Rev. B

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The temperature dependence of the electron-spin resonance linewidth in La0.95Sr0.05MnO3 has been determined and analyzed in the paramagnetic regime across the orbital ordering transition. From the temperature dependence and the anisotropy of linewidth and g-value the orbital order can be unambiguously determined via the mixing angle of the wave functions of the eg-doublet. The linewidth shows a similar evolution with temperature as resonant x-ray scattering results.PACS numbers: 77.22. Gm, 64.70.Pf In transition-metal oxides the orbital degrees of freedom play an important role for the electric and magnetic properties. Their coupling to spin, charge and lattice is responsible for the occurrence of a variety of complex electronic ground states. Orbital order (OO) can be derived via the Jahn-Teller (JT) effect or via superexchange (SE) between degenerate orbitals under the control of strong Hund's-rule coupling [1]. Strong correlations exist between spin and orbital order and between OO and lattice distortions, but of course a one-to-one correspondence cannot be expected. While spin and lattice order can easily be detected experimentally, this is not true for OO and so far the OO parameter remains hidden. In recent years resonant x-ray scattering (RXS) has been used to derive information on the OO parameter [2], but there is an ongoing dispute, whether RXS probes the JT distortion or the orbital charge distribution [3,4]. Indirectly, OO can also be derived from diffraction experiments via lattice distortions and bond lengths [5]. In this Letter we demonstrate that electron-spin resonance (ESR) can be used to detect OO and to monitor the evolution of the OO parameter. Probing the spin of the partially filled d-shell of Mn 3+ ions by ESR, the anisotropy and T -dependence of g-value and linewidth ∆H provide clear information on OO via spin-orbit (SO) coupling.The power of ESR to gain insight into OO will be demonstrated on A-type antiferromagnetic (AFM) LaMnO 3 (T N =140 K), the parent compound of the magneto-resistance manganites and a paradigm for a cooperative JT effect that suggests a d 3x 2 −r 2 /d 3y 2 −r 2 -type OO below T N =750 K [6]. However, it has been shown that SE interactions play an important role, too [7]. Several recent studies exhibit clear anomalies of the ESR parameters at the JT transition in both doped and pure LaMnO 3 [8,9,10,11]. The orbitally ordered O ′ -phase is characterized by an anisotropy of ∆H [11,12], which for polycrystalline samples reduces to a broad maximum in ∆H(T ) [9,10]. Previously, the angular dependencies of ∆H and the resonance field H res had been analyzed for 200 K and 300 K in high-temperature approximation, allowing to estimate the Dzyaloshinsky-Moriya (DM) interaction and the strength of the zero-field splitting (ZFS) parameters [13]. At X-Band frequencies (9 GHz) ∆H was of the same order of magnitude as H res and due to the overlap with the resonance at −H res and their mutual coupling via the nondiagonal elements of the dynamic susceptibility [14] the values for ...

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Anisotropic optical spectra in a detwinnedLaMnO3crystal

Cited by 98 publications

References 27 publications

VO ₂ : A two-fluid incoherent metal?

VO ₂ : A two-fluid incoherent metal?

Orbital ordering in manganites in the band approach

Orbital order parameter inLa0.95Sr0.05MnO3

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Anisotropic optical spectra in a detwinnedLaMnO3crystal

Cited by 98 publications

References 27 publications

VO 2 : A two-fluid incoherent metal?

VO 2 : A two-fluid incoherent metal?

Orbital ordering in manganites in the band approach

Orbital order parameter inLa0.95Sr0.05MnO3

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VO ₂ : A two-fluid incoherent metal?

VO ₂ : A two-fluid incoherent metal?