| Project/Area Number |
18540372
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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 |
Mathematical physics/Fundamental condensed matter physics
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| Research Institution | Kyoto University |
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Principal Investigator |
TOTSUKA Keisuke Kyoto University, Yukawa Institute for Theoretical Physics, Associate Professor (80291079)
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| Project Period (FY) |
2006 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥2,040,000 (Direct Cost: ¥1,800,000、Indirect Cost: ¥240,000)
Fiscal Year 2007: ¥1,040,000 (Direct Cost: ¥800,000、Indirect Cost: ¥240,000)
Fiscal Year 2006: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Keywords | Low-dimensional quantum spin systems / Multi-spin exchange interactions / Chiral orders / spin-nematic orders / Bse-Einstein condensation of spins / フラストレーション系 / 量子スピン系 / 多体交換相互作用 / マグノンBEC / スピンネマティック秩序 / 競合秩序 / 量子相転移 / sine-Gordon模型 / contractor renormaliz |
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| Research Abstract |
Construction of unifying theories for competing orders in one- and two dimensional quantum magnets which contain multi-spin exchange interactions. The effect of multi-spin exchange interactions (ring-exchange interaction, in particular) is intriguing in its own right since these interactions are thought of as diving hoes of many exotic quantum phases. We determined the global phase structures of ladder-type models which exhibit new kinds of phases (e.g. staggered dimer, staggered scalar chiral, nematic, etc.) from a unifying viewpoint based on high symmetries. Our analysis shows that the basic phase structure of these systems can be understood by considering effective Bose liquids with spins (S=1). We also extended our methods to two-dimensional cases by using the contractor-renormalization (CORE) method.
A first step toward the understanding of the ground-state phases of spin-1 triangular lattice antiferromagnets. The discovery of a new spin-1 two-dimensional antiferromagnet on a triangular lattice sparked interests on various ground-state phases in S=1 triangular-lattice antiferromagnets. We stripped off a one-dimensional subset (zigzag ladder) and investigated the phase diagram by a combined use of large-scale numerical simulations and field-theoretical methods.
Magnetism of a new two-dimensional spin-gap compound (CuCl)LaNb_2O_7. The Cu-based compound (CuCl)LaNb_2O_7 exhibits a finite spin gap above a singlet ground state and undergoes a spin-Bose-Einstein condensation (BEC) when strong enough field is applied. According to the standard theory of spin-BEC, the observed spin gap and the critical field, at which spin-BEC mass, seem inconsistent with each other. We proposed a new scenario that BEC occurs in spin-quintet channel to explain magnetism of this compound. The most remarkable feature of this new kind of spin-BEC is that the transverse magnetization vanishes even after the onset of magnetization.
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