Variation of optical gaps in perovskite-type 3<i>d</i>transition-metal oxides

Arima, T.; Tokura, Y.; Torrance, J. B.

doi:10.1103/physrevb.48.17006

Cited by 600 publications

(458 citation statements)

References 16 publications

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“…These superlattice peaks were confirmed in a powder sample study, one such 2θ scan is shown in Figure 6. The intensities of these halfinteger points, and the missing intensities of the 1/2(hhh) superlattice points, are well fit by a simple model for the structure factor of such points given by Axe et al [17] for LaAlO 3 . We can therefore see that the distortion is due to rotations of the MO 6 oxygen octahedra along each (111) axis to obtain a rhombohedral symmetry or an R 25 phonon condensation.…”

Section: Magnetismmentioning

confidence: 82%

“…Since the discovery of the high temperature superconducting copper oxides, study of these hole-doped manganese oxides has seen a revival. This renewed interest is due partly to the fact that LaMnO 3 is a charge gap insulator [3] associated with the large correlation energy of the d electrons in the e g band, and also to the discovery of giant magnetoresistance phenomena in samples with Sr dopant densities in the 0.2 ≤ x ≤ 0.4 regime [4,5]. The structural phase transition can also be induced by magnetic fields when the doping level is near x ≈ 0.17 [6].…”

Section: Introductionmentioning

confidence: 99%

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Magnetism and structural distortion in theLa0.7Sr0.3Mn
Martin
¹
,
Shirane
²
,
Endoh
³

et al. 1996
Phys. Rev. B
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Neutron scattering studies on a single crystal of the highly-correlated electron system, La 1-x Sr x MnO 3 with x ≈ 0.3, have been carried out elucidating both the spin and lattice dynamics of this metallic ferromagnet. We report a large measured value of the spin wave stiffness constant, which directly shows that the electron transfer energy of the d band is large. The spin dynamics, including magnetic critical scattering, demonstrate that this material behaves similar to other typical metallic ferromagnets such as Fe or Ni. The crystal structure is rhombohedral, as previously reported, for all temperatures studied (below ~425K). We have observed new superlattice peaks which show that the primary rhombohedral lattice distortion arises from oxygen octahedra rotations resulting in an R 3c structure. The superlattice reflection intensities -which are very sensitive to structural changes -are independent of temperature demonstrating that there is no primary lattice distortion anomaly at the magnetic transition temperature, T c = 378.1 K, however there is a lattice contraction.

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Section: Magnetismmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Magnetism and structural distortion in theLa0.7Sr0.3Mn
Martin
¹
,
Shirane
²
,
Endoh
³

et al. 1996
Phys. Rev. B
Self Cite
302
15
150
1
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“…For YTiO 3 , YVO 3 , and LaVO 3 there is a good agreement with the experimental optical data. 15,65 However, for LaTiO 3 the experimental gap is much smaller (∼0.1 eV). 65 This may indicate again at the particular importance of correlation effects in LaTiO 3 .…”

Section: E Spin-orbit Interaction and Magnetic Ground Statementioning

confidence: 99%

Lattice distortion and magnetism of3d−t2gperovskite oxides

Solovyev

2006

Phys. Rev. B

150

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Several puzzling aspects of interplay of the experimental lattice distortion and the the magnetic properties of four narrow t2g-band perovskite oxides (YTiO3, LaTiO3, YVO3, and LaVO3) are clarified using results of first-principles electronic structure calculations. First, we derive parameters of the effective Hubbard-type Hamiltonian for the isolated t2g bands using newly developed downfolding method for the kinetic-energy part and a hybrid approach, based on the combination of the random-phase approximation and the constraint local-density approximation, for the screened Coulomb interaction part. Apart form the above-mentioned approximation, the procedure of constructing the model Hamiltonian is totally parameter-free. The results are discussed in terms of the Wannier functions localized around transition-metal sites. The obtained Hamiltonian was solved using a number of techniques, including the mean-field Hartree-Fock (HF) approximation, the second-order perturbation theory for the correlation energy, and a variational superexchange theory, which takes into account the multiplet structure of the atomic states. We argue that the crystal distortion has a profound effect not only on the values of the crystal-field (CF) splitting, but also on the behavior of transfer integrals and even the screened Coulomb interactions. Even though the CF splitting is not particularly large to quench the orbital degrees of freedom, the crystal distortion imposes a severe constraint on the form of the possible orbital states, which favor the formation of the experimentally observed magnetic structures in YTiO3, YVO3, and LaVO3 even at the level of mean-field HF approximation. It is remarkable that for all three compounds, the main results of all-electron calculations can be successfully reproduced in our minimal model derived for the isolated t2g bands. We confirm that such an agreement is only possible when the nonsphericity of the Madelung potential is explicitly included into the model. Beyond the HF approximation, the correlations effects systematically improve the agreement with the experimental data. Using the same type of approximations we could not reproduce the correct magnetic ground state of LaTiO3. However, we expect that the situation may change by systematically improving the level of approximations for dealing with the correlation effects.

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“…From experiments and band calculations, t 0 is considered to be around 0.5 eV andŨ is estimated at several eV. 13,15,14,45,46,47) In the present study, we changeŨ /t 0 as a parameter and discuss its realistic value based on our results. The spring constant k is roughly estimated by the frequency of an oxygen bond stretching phonon at order of 10 or 100 eV.…”

mentioning

confidence: 99%

“…In particular, we focus here the following: (i) All the materials are the Mott insulator with a charge gap of order of eV at half filling (one e g electron per Mn site on average), where two-dimensional (2D) anisotropy realizes in spin and orbital orderings, and a cooperative JahnTeller (JT) distortion. 7,11,12,13,15,14) (ii) Upon doping of holes, a metal-insulator (MI) transition occurs from the anisotropic Mott insulator to an isotropic ferromagnetic metal through disordered ferromagnetic insulator. 6,9,16) (iii) In the ferromagnetic metallic state, charge dynamics shows strong incoherence with tiny Drude weight even at low temperatures while the linear specific-heat coefficient γ remains small.…”

mentioning

confidence: 99%

Effects of Electron Correlation, Orbital Degeneracy and Jahn-Teller Coupling in Perovskite Manganites

Motome

Imada

1999

J. Phys. Soc. Jpn.

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Roles of Coulomb interaction, orbital degeneracy and Jahn-Teller coupling in double-exchange models are examined for Mn perovskite oxides. We study the undoped Mott insulator as well as metal-insulator transitions by hole doping, and especially strong incoherence of ferromagnetic metal. We derive models where all the spins are fully polarized in two-dimensional planes as in the experimental indications, and investigate their ground-state properties by quantum Monte Carlo method. At half filling where the number of eg electron is one per site on average, the Coulomb interaction opens a Mott gap and induces a staggered orbital ordering. The opening of the Mott gap is, however, substantially slower than the mean-field results if the Jahn-Teller coupling is absent. The synergy between the strong correlation and the Jahn-Teller coupling largely enhances the Mott gap amplitude and reproduces realistic amplitudes and stabilization energy of the Jahn-Teller distortion. Upon doping, the orbital ordering stabilized by the Coulomb interaction is destroyed immediately. Toward the metal-insulator transition, the short-ranged orbital correlation is critically enhanced in metals, which should be related to strong incoherence of charge dynamics observed in experiments. Our model, moreover, exhibits a uniform ordering of d x 2 −y 2 orbital in a wide region of doping in agreement with experimental indications.KEYWORDS: perovskite manganites, double exchange model, Coulomb interaction, orbital degeneracy, JahnTeller coupling, Mott gap, orbital ordering, Jahn-Teller distortion, metal-insulator transition, ferromagnetic metal, incoherent charge dymanics, quantum Monte Carlo method 'Simple' double-exchange (DE) models, that is, models with a single non-interacting conduction band ferromagnetically coupled with localized spins, have been intensively studied 1, 2, 3, 4, 5) to understand physical properties of Mn perovskite oxides, especially collosal magnetoresistance. 6,7,8,9,10) These models have successfully explained several experimental aspects at least qualitatively; for instance, ferromagnetic metals in a hole-doped region with a transition to a paramagnetic state by raising temperature, and a large negative magnetoresistance near the transition. All these properties are due to the so-called double-exchange mechanism; doped holes tend to gain kinetic energy by aligning localized spins in parallel. 1, 2, 3)However, many open problems still remain. In particular, we focus here the following: (i) All the materials are the Mott insulator with a charge gap of order of eV at half filling (one e g electron per Mn site on average), where two-dimensional (2D) anisotropy realizes in spin and orbital orderings, and a cooperative JahnTeller (JT) distortion. 7,11,12,13,15,14) (ii) Upon doping of holes, a metal-insulator (MI) transition occurs from the anisotropic Mott insulator to an isotropic ferromagnetic metal through disordered ferromagnetic insulator. 6, 9, 16) (iii) In the ferromagnetic metallic state, charge dynamics shows strong inco...

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Variation of optical gaps in perovskite-type 3dtransition-metal oxides

Cited by 600 publications

References 16 publications

Magnetism and structural distortion in theLa0.7Sr0.3Mn
Martin
¹
,
Shirane
²
,
Endoh
³

et al. 1996
Phys. Rev. B
Self Cite
302
15
150
1
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Magnetism and structural distortion in theLa0.7Sr0.3Mn
Martin
¹
,
Shirane
²
,
Endoh
³

et al. 1996
Phys. Rev. B
Self Cite
302
15
150
1
View full text Add to dashboard Cite

Lattice distortion and magnetism of3d−t2gperovskite oxides

Effects of Electron Correlation, Orbital Degeneracy and Jahn-Teller Coupling in Perovskite Manganites

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Variation of optical gaps in perovskite-type 3dtransition-metal oxides

Cited by 600 publications

References 16 publications

Magnetism and structural distortion in theLa0.7Sr0.3MnMartin1, Shirane2, Endoh3 et al. 1996Phys. Rev. BSelf Cite302151501View full textAdd to dashboardCite

Magnetism and structural distortion in theLa0.7Sr0.3MnMartin1, Shirane2, Endoh3 et al. 1996Phys. Rev. BSelf Cite302151501View full textAdd to dashboardCite

Lattice distortion and magnetism of3d−t2gperovskite oxides

Effects of Electron Correlation, Orbital Degeneracy and Jahn-Teller Coupling in Perovskite Manganites

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Product

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Magnetism and structural distortion in theLa0.7Sr0.3Mn
Martin
¹
,
Shirane
²
,
Endoh
³

et al. 1996
Phys. Rev. B
Self Cite
302
15
150
1
View full text Add to dashboard Cite

Magnetism and structural distortion in theLa0.7Sr0.3Mn
Martin
¹
,
Shirane
²
,
Endoh
³

et al. 1996
Phys. Rev. B
Self Cite
302
15
150
1
View full text Add to dashboard Cite