| Project/Area Number |
14540336
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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 | Osaka University |
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Principal Investigator |
SUGA Sei-ichiro Osaka University, Department of Applied Physics, Associate Professor, 大学院・工学研究科, 助教授 (40206389)
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| Project Period (FY) |
2002 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 2004: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2003: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2002: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Keywords | S=1 bond-alternating spin chain / dynamical structure factor / transverse magnetic fields / Tomonaga-Luttinger liquid / NMR relaxation rate / incommensurate magnetic order / optical absorption spectra / Kondo insulator / 垂直磁揚 / ハルデーンギャップ / 数値厳密対角化 / 動的平均場近似 / 量子相転移 / フラストレートしたS=1 / 2ボンド交替鎖 / 磁場中での臨界的性質 / S=1ボンド交替鎖 / S=1 / 2スピン梯子 / 4体スピン相互作用 / 重い電子系 / 非フェルミ流体 / 乱れた系 / 量子モンテカルロ法 |
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| Research Abstract |
(1) Dynamical properties of S=1 bond-alternating spin chains in transverse fields
S=1 bond-alternating spin chains exhibit a quantum phase transition between the Haldane-gap phase and the dieter phase depending on the bond-alternating ratio. Recent inelastic neutron-scattering experiments revealed that typical compounds in respective phases NDMAP and NTENP show different dynamical properties in transverse magnetic fields. We have calculated dynamical structure factors of NDMAP and NTENP in transverse magnetic fields. From the analysis of field dependence of the one-magnon isolated model and the excitation continuum, we have shown that the characteristic field dependence results in the different field dependence of the excitation continuum.
(2) Field-induced incommensurate state in frustrated S=1/2 bond-alternating spin chains in magnetic fields
In a typical S=1/2 bond alternating spin-chain compound F_5PNN, non-trivial temperature dependence of the NMR relaxation rate was observed in magn
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etic fields. We have investigated critical properties of the system in magnetic fields by introducing the next-nearest-neighbor interaction, and explained the experimental findings in viewpoint of the Tomonaga-Luttinger liquid. Furthermore, taking account of the interchain interaction by mean field theory, we have shown that the incommensurate ordered state takes place around the half-value of the magnetization saturation.
(3) Optical absorption spectra in S=1/2 spin ladders
Optical absorption spectra in S=1/2 two-leg spin ladders are investigated by the RVB description and the numerical diagonalization method. We have shown that the shoulder structure caused by the cyclic four spin interaction appears in addition to the ordinary two-mignon peak. On the basis of the numerical results, the frequencies for the shoulder and peak of a typical compound SrCu_2O_3 are evaluated.
(4) Field induced phase transition in Kondo insulator
On the basis of the periodic Anderson model, we have obtained the temperature field phase diagram of the Kondo insulator, combining dynamical-mean-field theory and quantum Monte Carlo technique. As field is increased in low temperatures, the phase transition among Kondo insulator-antiferromagnet-spin polarized metal occurs. Slightly above the antiferromagnetic transition temperature, heavy-fermion states with the enhanced mass are realized. Its origin was discussed in viewpoint of the one particle spectrum and the dynamical spin susceptibility. Less
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