1998 Fiscal Year Final Research Report Summary
NMR Studies of Quantum Choherence and Magnetism in Spin-Ladder Systems
| Project/Area Number |
09440138
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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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 |
KITAOKA Yoshio Graduate School of Engineering Science, Professor, 基礎工学研究科, 教授 (70110707)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIDA Kenji Graduate School of Engineering Science, Research Associate, 基礎工学研究科, 助手 (90243196)
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| Project Period (FY) |
1997 – 1998
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| Keywords | Spin Ladder, / Quantum Spin System, / Spin Liquid, / Spin Gap, / Quantum Criticality, / NMR / NQR, / Impurity Effect / 量子臨界現象 |
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| Research Abstract |
This research project was planed to investigate by means of NMR/NQR the quantum coherence and anoma-lous magnetism in S=1/2 spin-ladder systems through the impurity and carrier doping effects.
Characteristics of impurity (Zn, Ni, and La)-induced staggered polarization (IISP) and antiferromagnetic long-range order (AF-LRO) were clarified in gapped spin-1/2 Heisenberg two-leg ladder compound SrCu^2O^3. A correlation length xi^3/a estimated from a quasi-one-dimensional (Q1D) IISP along the two-leg was found to be much longer even in x=0.001 and 0.005 than xi^0/a. The T-independent xi^3/a is scaled to an average distance D^<AV> = 1/(2x) in the Zn and Ni doping and D^<AV> = 1/x in the La doping between the impurities, for example, xi^0/a -50 is estimated in the Zn doping when D^<AV> = 500 for x=0.001. The significantly broadened NQR spectrum has unambiguously identified the appearance of AF moments associated with the AF-LRO in the Zn and Ni doping. Rather uniform AF moments around the middl
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e Cu sites between the impurities are estimated to be in an order of 0.04 mubeta at 1.4 K with their direction along the a axis. The spatial variation of AF moments is shown to be of exponential type with almost the same xi^0/a = 8 (x=0.01) and 4.5 (x=0.02) as in the LISP for the Zn doping. The Q1D-IISP was found to be dramatically enhanced by an interladder interaction even though so weak, once the impurity breaks up the quantum coherence in the short-range resonating valence bond (RVB) state with the gap. On the other hand, we propose that T^N is determined by a strength of the interladder interaction and a size of S^o. We showed that hole-doped two-leg ladder compound Sr^<2.5>Ca^<11.5>Cu^<24>O^<41> comprising Cu^2O^3 ladders and CuO^2 chains reveals three dimensional (3D) magnetic order below T^M=2.2 K.We found that small moments - 0.02 mubeta are spontaneously ordered on the ladders, whereas large moments - 0.56mubeta or the magnetic Cu sites occupying about one-fourth of the chains. It is suggested that this 3D magnetic order is a cooperative phenomenon driven by the formation of pinned CDW-like state on the ladders which the optical conductivity measurement has clarified. Less
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Research Products
(18 results)
