Browsing by Author "Tanaka, A"

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Anomalous spin polarization and dualistic electronic nature of CrO(2)
(2003-06-01)
Huang, DJ
;
Tjeng, LH
;
Chen, J
;
Chang, CF
;
Wu, WP
Spin-resolved O 1s x-ray absorption measurements on CrO(2) reveal that the spin polarization of the states at the Fermi level approaches 100%, providing direct evidence of the half-metallic nature of CrO(2). The measurements also show the existence of an atomiclike Cr 3d state not far away from the Fermi level with a spin polarization of only 50%, establishing its Mott-Hubbard character. We conclude that CrO(2) has a dualistic electronic nature, in which the states at the Fermi level are bandlike, while those at higher energies are strongly localized of completely different origin and symmetry. The finding of an exceptionally large number of O 2p holes suggests their important role in preventing the strongly correlated CrO(2) from being an insulator.
Anomalous spin polarization and dualistic electronic nature of CrO2
(2003-06-01)
Huang, DJ
;
Tjeng, LH
;
Chen, J
;
Chang, CF
;
Wu, WP
Spin-resolved O 1s x-ray absorption measurements on CrO2 reveal that the spin polarization of the states at the Fermi level approaches 100%, providing direct evidence of the half-metallic nature of CrO2. The measurements also show the existence of an atomiclike Cr 3d state not far away from the Fermi level with a spin polarization of only 50%, establishing its Mott-Hubbard character. We conclude that CrO2 has a dualistic electronic nature, in which the states at the Fermi level are bandlike, while those at higher energies are strongly localized of completely different origin and symmetry. The finding of an exceptionally large number of O 2p holes suggests their important role in preventing the strongly correlated CrO2 from being an insulator.
Magnetic circular dichroism in Fe 2p resonant photoemission of magnetite
(2004-02-01)
Chen, J
;
Huang, DJ
;
Tanaka, A
;
Chang, CF
;
Chung, SC
Measurements of magnetic circular dichroism in Fe 2p resonant photoemission and calculations based on a full-multiplet cluster model reveal the parameters of the electronic structure of Fe3O4. We obtained on-site Coulomb energy U-dd of 3d electrons, charge-transfer energy Delta which is defined as the energy required to transfer an electron from O 2p to Fe 3d, and the hybridization strength between Fe 3d and O 2p at different Fe ion sites of Fe3O4 by analyzing the data of magnetic circular dichroism. The charge-transfer energy of Fe3+ ions was found to be significantly smaller than that of Fe2+ ions. We determined the energy positions of the low-lying multiplets of each Fe ion site. These energy positions for Fe3+ ion sites are 1.5-2.5 eV higher than those obtained from band-structure calculations. Our calculations also show that the photoemission spectral weight in binding energy bigger than 10 eV is substantial, in contrast to the results of band-structure calculations. Our findings conclude that Fe3O4 is a system with strong electron-electron interactions.
Orbital ordering in La0.5Sr1.5MnO4 studied by soft x-ray linear dichroism
(2004-02-27)
Huang, DJ
;
Wu, WB
;
Guo, GY
;
Lin, HJ
;
Hou, TY
We found that the conventional model of orbital-ordering of 3x(2)-r(2)/3y(2)-r(2) type in the e(g) states of La0.5Sr1.5MnO4 is incompatible with measurements of linear dichroism in the Mn 2p-edge x-ray absorption, whereas these e(g) states exhibit predominantly cross-type orbital ordering of x(2)-z(2)/y(2)-z(2). LDA+U band-structure calculations reveal that such a cross-type orbital-ordering results from a combined effect of antiferromagnetic structure, Jahn-Teller distortion, and on-site Coulomb interactions.
Orbital polarization of LaSrMnO4 studied by soft X-ray linear dichroism
(2004-07-01)
Wu, WB
;
Huang, DJ
;
Guo, GY
;
Lin, H
;
Hou, TY
With polarization-dependent soft X-ray absorption, we determined the orbital character of occupied and the lowest unoccupied e, orbitals of prototype single-layered perovskite LaSrMnO4, Our measurements indicate that LaSrMnO4 exhibits strong orbital polarization in the e, states of Mn3+ sites, leading us to conclude that LaSrMnO4 has a "ferro-orbital" ordering of 3z(2)-r(2). We found that linear dichroism in soft X-ray absorption is an effective experimental method to identify the nature of orbital ordering in transition-metal oxides such as manganites. (C) 2004 Elsevier B.V. All rights reserved.
Orbital symmetry and electron correlation in NaxCoO2
(2005-04-15)
Wu, WB
;
Huang, DJ
;
Okamoto, J
;
Tanaka, A
;
Lin, HJ
Measurements of polarization-dependent soft x-ray absorption reveal that the electronic states determining the low-energy excitations of NaxCoO2 have predominantly a(1g) symmetry with significant O 2p character. In contrast to the prediction of band theory, doping-dependent O 1s x-ray absorption shows a large transfer of spectral weight, providing spectral evidence for strong electron correlations of the layered cobaltates. We also found that NaxCoO2 exhibits a charge-transfer electronic character rather than a Mott-Hubbard character.