2000 Fiscal Year Final Research Report Summary
Dynamical theory for fluctuations and phase transitions in orbitally degenerate electron systems
| Project/Area Number |
10640327
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | Tohoku University |
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Principal Investigator |
KURAMOTO Yoshio Graduate School of Science, Tohoku University, Professor, 大学院・理学研究科, 教授 (70111250)
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| Co-Investigator(Kenkyū-buntansha) |
KUSUNOSE Hiroaki Graduate School of Science, Tohoku University, Research Associate, 大学院・理学研究科, 助手 (00292201)
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| Project Period (FY) |
1998 – 2000
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| Keywords | orbital degeneracy / quadrupole order / fluctuation / effective medium theory / elastic constants |
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| Research Abstract |
Formulation of theoretical framework with account of orbital fluctuations We extended the mean-field theory to take account of fluctuation effects. The new theory becomes exact in the limit of infinite spatial dimensions, and is regarded as a quantummechanical extension of the spherical model approximation for classical spins. Our theory goes one step beyond the other ones that use localized fermions to represent spins.
Explanation of the strange order in orbitally degenerate electron systems such as CeB_6 and Ce_<0.75>La_<0.25>B_6
We explained origin of strange magnetic order in the phase III of CeB_6 by assuming a pseudo-dipolar interaction between next-nearest-neighbor sites. Furthermore, we discussed possibility of an octupole order for the newly found phase IV in Ce_<0.75>La_<0.25>B_6. We found a new plase which lies energetically close to the already observed phases, and which may be realized in the presence of external field such as uniaxial pressure. We developed new functional i
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ntegral formalism to perform the Ginzburg-Landau expansion microscopically.
Spin and orbital wave excitations in orbitally degenerate electron systems
We derived the dispersion relations of elementary excitations from the complicated spinorbital ordered state. The large unit cell with 16 Ce ions give rise to 48 branches. We derived all branches and found characteristic relation between the spectrum and the multipolar interaction. In particular some branches are almost flat along certain directions of wave vector, which may be checked by neutron diffraction.
Exact dynamics of orbitally degenerate one-dimensional systems
So far we explained results for three-dimensional systems. In low dimensions, the role of fluctuations is much more important. In order to see the situation most clearly, we studied an exactly soluble model in one dimension. This model has the SU (4) symmetry to represent the degeneracy, and the interaction is inversely proportional to the square of the distance (1/γ^2). We succeeded in deriving the dynamical correlation function exactly. Less
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