| Project/Area Number |
12640366
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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 |
物性一般(含基礎論)
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| Research Institution | CHIBA UNIVERSITY |
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Principal Investigator |
NATSUME Yuhei UNDERGRADUATE SCHOOL OF SCIENCE AND TECHNOLOGY, CHIBA UNIVERSITY, PROFESSOR, 大学院・自然科学研究科, 教授 (80114312)
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| Co-Investigator(Kenkyū-buntansha) |
NAKAYAMA Takashi DEPARTMENT OF PHYSICS, FACULTY OF SCIENCE, CHIBA UNIVERSITY, PROFESSOR, 理学部, 教授 (70189075)
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| Project Period (FY) |
2000 – 2001
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| Project Status |
Completed (Fiscal Year 2001)
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| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2001: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2000: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Keywords | EXCHANGE SCATTERING / MAGNETIC RAMAN SPECTRA / SINGLET GRIND STATE / QUANTUM ANTIFERROMAGNETS / LADDER HEISENBERG SYSTEM / TRIPLET DIMERS / REPRODUCTION OF SPECTRA / EXACT DIAGONALIZATION / 梯子構造反強磁性体 / 量子スピン系 / シングレット基底状態 / トリプレット対の励起 |
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| Research Abstract |
The low-dimensional antiferromagnetic systems have quite characteristic features. In fact, much work for ground states has been made up to now. On the other hand, optical properties of low-lying excited states on spin-gaps in these systems have been reported by relatively small number of papers. In particular, the magnetic Raman-scattering has been discussed by only a few papers. In the present investigation, we reproduce spectra for the exchange-scattering mechanism in two-leg ladder quantum antiferromagnetic systems by the numerical calculation. We treat the finite Heisenberg ladders, in which legs with antiferromagnetic bonds J_c are connected by rungs with antiferromagnetic, bonds J_r. The calculation is made in the system of 50 x 2 sites with spin=1/2 by the perturbation method for the extension of J_c/J_r, in addition to that in 12 x 2 by the exact diagonalization. The singlet ground states are expressed as the oderings of singlet dimers on rungs for small value of J_c/J_r, while excited states can be described as the patterns for triplet dimers on rungs. In fact, we can make clear the origin of the characteristic shapes of magneitc Raman spectra observe at twice the spin-gaps in C_aV_2O_5. Namely, this asymmetric shape is explained by the fact that the corresponding excited states with large transition moments are composed of patterns of pairs for triplet dimers on adjacent rings. The agreement between the present calculation and the observed spectra is quite well. Furthermore, we investigate magnetic Raman spectra in two-leg ladder systems Sr_<14-x>Ca_xCu_<24>O_<41> with relatively large values of J_c/J_r. By the present analyzes of magnetic Raman spectra in low-dimensional quantum antiferromagnetic systems, we can propose the powerful method for understanding properties of excited states and the origin of spin-gaps.
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