2005 Fiscal Year Final Research Report Summary
Effect of orbital degeneracy on the heavy electron systems
| Project/Area Number |
14540325
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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 | The University of Tokyo |
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Principal Investigator |
UEDA Kazuo The University of Tokyo, Institute for Solid State Physics, Professor, 物性研究所, 教授 (70114395)
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| Project Period (FY) |
2002 – 2005
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| Keywords | orbital degeneracy / heavy electron system / orbital fluctuation / superconductivity / itinerant ferromagnetism / Hund rule / trans Uranium compound / frustration |
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| Research Abstract |
In the heavy electron systems, a characteristic energy scale called a Kondo temperature is small and thus it is possible to controll artificially phase transition between an antiferromagnetic phase and a superconductive phase. Understanding of this type of quantum critical behaviors is a main theme of the current research of condensed matter physics. The main objective of this study was to clarify the role of orbital degeneracy concerning the quantum phase transition. For this study we used a j-j coupling scheme, since the important effect of electron-electron interaction may be treated by a perturbation theory in a systematic way. The main results obtained through the present study may be summarized as follows :
(1) We have developed an effective Hamiltonian for the Ce115 system based on the j-j coupling scheme and clarified its magnetic as well as superconductive properties. Electronic states of PuCoGa_5, which is a newly found superconductor, are studied by electronic band structure calculations.
(2) Heavy electron behaviors are reported for LiV_2O_4 which is a transition metal compound. To understand the origin of the heavy mass, an extended Hubbard type model was considered on the pyrochlore lattice taking account of the orbital degeneracy. Nature of spin, orbital, and spin-orbital combined fluctuation modes of the model are clarified.
(3) Concerned with the origin of the superconductivity observed in UGe_2, possibility of the first order phase transition between two uniform ferromagnetic phases was investigated for a model constructed for UGe_2. It has turned out that this type of transition is possible due to the effect of orbital degeneracy.
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