The study on a new quantum-spin phase in a quantum ladder system
| Project/Area Number |
11640355
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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 | KYUSHU INSTITUTE OF TECHNOLOGY |
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Principal Investigator |
DEGUCHI Hiroyuki Kyushu Inst.Tech., Faculty of Engineering, Associate prof., 工学部, 助教授 (30192206)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAGI Seishi Kyushu Inst.Tech., Faculty of Engineering, Professor, 工学部, 教授 (90112359)
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| Project Period (FY) |
1999 – 2000
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| Project Status |
Completed (Fiscal Year 2000)
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| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2000: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1999: ¥2,800,000 (Direct Cost: ¥2,800,000)
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| Keywords | spin ladder / random-bond / susceptibility / magnetization / Griffiths phase / Cu_2(C_5H_<12>N_2)_2(Cl_<1-x>Br_x)_4 / スピンギャップ / 量子スピン相 / 非フェルミ液体 / ランダムシングレット相 / ランダムボンド |
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| Research Abstract |
New quantum antiferromagnetic chains, spin-ladder systems, have attracted a lot of theoretical and experimental interest. An even-leg ladder is believed to be a spin-gap system and to have a short-range resonating valence bond (RVB) ground state. The compound Cu_2 (C_5H_<12>N_2)_2Cl_4 (hereafter, CHpC) is a typical two-leg ladder system with exchange interaction for the rungs (J_⊥ /k=13.2K) and for the legs (J _<//>/k=2.4K) of the ladder and a spin-gap energy of Δ/k=l0.5K.Recently, we reported experimental results of a new compound Cu_2(C_5H_<12>N_2)_2Br_4 (hereafter, CHpB) of which crystal structure is isostrucural with CHpC.The results suggest that the compound CHpB is a spin-ladder system with a spin-gap like CHpC.We estimated the exchange interactions J _⊥/k=24.8K, J _<//>/k=3.5K and a spin-gap energy of Δ/k=21.3K.Therefore, the random mixture compound Cu_2(C_5H_<12>N_2)_2 (Cl_<1-x>Br_x)_4 seems to be a ladder system with random antiferromagnetic bonds. The magnetic properties of a
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random mixture compound Cu_2(C_5H_<12>N_2)_2 (Cl_<1-x>Br_x)_4 are rather different from those of the pure systems. Paramagnetic divergence is significantly observed for the susceptibility at low temperatures and the magnetization appears even at low fields. For random systems, the susceptibilities do not follow the Curie law and diverge stronger than the Curie law. The systems with strong randomness are in a random singlet phase or are in a Griffice phase of which susceptibility diverges at low temperatures. The heat capacity of both pure and random systems was measured at low temperatures. In the cases of pure systems, the behavior of heat capacities is of the exponential type T^2exp (-Δ/kT), where Δ is the gap energy for the collective excitation. For random systems, the heat capacity at low temperatures shows similar behavior observed for pure systems in applied field, of which gap energy decreases with increasing H.
The results suggest that the ground state of the random-bond ladder is a Griffiths phase. Less
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Report
(3 results)
Research Products
(12 results)
