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CNagao, Tatsuya*; Igarashi, Junichi
Physica B; Condensed Matter, 345(1-4), p.70 - 73, 2004/03
Times Cited Count：1 Percentile：7.1(Physics, Condensed Matter)To investigate the effect of the lattice distortion on the resonant X-ray scattering (RXS) spectra in DyBC, we study the crystal electric field Hamiltonian to fit the low-lying level scheme. By using the quasi-quartet ground states of the Hamiltonian, we analyze the cooperative Jahn-Teller effect at absolute zero. We find that a certain type of buckling of sheets of B and C atoms is an energetically favored state. This naturally leads to a canted quadrupole ordering phase consistent with the experiment. We show that the obtained lattice distortion gives rise to large intensities on RXS spectra around the Dy L
edge by modulating 5d bands.
Hotta, Takashi
Physical Review B, 67(10), p.104428_1 - 104428_8, 2003/03
Times Cited Count：21 Percentile：68.18(Materials Science, Multidisciplinary)The existence of a novel metal-insulator transition in the ferromagnetic state of models for undoped manganites is here discussed using numerical techniques applied to the 
-orbital degenerate Hubbard model tightly coupled with Jahn-Teller distortions. The ground-state phase diagram is presented in the plane defined by the electron-phonon coupling 
and Coulomb interaction 
. In contrast to the standard one-band Hubbard model for cuprates, the metallic phase is found to exist for finite values of both and in the present -orbital Hubbard model even at half-filling, due to the Fermi-surface topology which is incompatible with the staggered orbital ordering concomitant to the insulating phase. Based on the present results, a possible scenario for Colossal Magneto-Resistive effect is discussed in undoped manganites.
