1996 Fiscal Year Final Research Report Summary
NMR Study on the Quantum Effect of Low Dimensional Spin System under High Magnetic Fields
| Project/Area Number |
07640474
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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 | KYOTO UNIVERSITY |
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Principal Investigator |
CHIBA Meiro Institute of Advanced Energy Advanced Energy Generation Division Quantum Radiation Energy Research Section Kyoto University, エネルギー理工学研究所, 助教授 (90027144)
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| Project Period (FY) |
1995 – 1996
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| Keywords | spin-gap / quantum effect / one-dimensional / antiferromagnet / Haldane-gap / bond-alternation |
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| Research Abstract |
The quantum spin effect is one of the most interesting subjects in the physics of magnetism at low temperatures. Of these, the quantum spin-gap attracts much attention. Various origins of the spin-gap are known and they are classified into two categories. The one is due to the single or two-spin origin, such as single ion anisotropy, antiferromagnetic (AF) coupled spin pair, etc. The other is due to many body quantum spin origin in one-dimensional AF linear chain, such as the Haldane effect, the spin-Peierls transition etc.
Above all, the quantum spin-gap due to the many body spin effect in one-dimensional antiferromagnet has become an exciting problem, when Haldane has predicted the existence of the spin-gap in one-dimensional Heisenberg antiferromagnet with integer spin. Until that time, it was believed that the spin-gap did not exist in such a system. The exact theoretical solution of S=1/2 Heisenberg AF chain shows no spin-gap between the ground state and the first excited state. Si
… More
nce it was considered that the quantum spin effect should be expected most clearly in S=1/2 system, Haldane's prediction was sensational. Since then, many theoretical and experimental works have been performed to reveal that the Haldane conjecture is true.
It should be noted that the S=1/2 uniform Heisenberg AF chain has no spin-gap, while that the chain with bond alternation has a spin-gap. On the quantum spin-gap in the S=1/2 Heisenberg AF chain with bond alternation, the first observation of the spin-Peierls transition has recently been reported in an inorganic material CuGeO_3. The SP-phase, which has a spin-gap, is a one-dimensional AF chain with bond alternation. In order to clarify the spin-gap in SP-phase we have made an NMR experiment on CuCl_2 (gamma-picoline) _2, which has crystallographic bond alternation.
These spin-gaps have been studied through NMR experiments. The spin echo spectrum and the nuclear spin-lattice relaxation under high magnetic fields have been performed and compared. Less
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