2007 Fiscal Year Final Research Report Summary
Probing exotic orders in quantum magnets through Berry phases
| Project/Area Number |
18540386
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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 | National Institute for Materials Science |
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Principal Investigator |
AKIHIRO Tanaka National Institute for Materials Science, Computational Materils Science Center, Senior Researcher (10354143)
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| Co-Investigator(Kenkyū-buntansha) |
KOHNO Masanori National Institute for Materials Science, Computational Materials Science Center, Senior Researcher (40370308)
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| Project Period (FY) |
2006 – 2007
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| Keywords | Berry phases / quantum antiferromagnets / effective field theory / spinons / Bethe ansatz / magnetization plateau / lattice gauge theory |
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| Research Abstract |
(1) We have derived a new effective field theory with a topological term (theta-term) which can detect spin gap phases and quantum phase transitions in antiferromagnets in 2 and 3 spatial dimensions. We expect that this theory, which is a natural generalization of the Haldane-Affleck mapping of 1d antiferromagnets to a nonlinear sigma with a theta-term, can be utilized in the search for exotic spin liquid states.
(2) In collaboration with researchers in Santa Barbara and Utah, one of us (MK) has resolved the issue on the theoretical understanding on the nature of the spinon excitations observed experimentally in the 2d compound Cs_2CuCl_4. The theory models the system as composed of weakly coupled antiferromagnetic spin chains, and reproduces well the experimental results. This finding implies that the spinons in this compound are best understood to be descendent s of the conventional spinon excitations which exist in Id. systems.
(3) In collaboration with K. Totsuka of the Yukawa Institute, Kyoto University, the Head Investigator of this project investigated the magnetization process of antiferromagnets in an external magnetic field. We found that spacetime vortices of the spin components lying within the plane normal to the field contributes nontrivial Berry phases which doinate the low energy physics. The Berry phase effect reproduces known results for ld, provides natural extensions to 2 and 3d, and also under certain conditionsmaps the system into a lattice gauge theory which gives rise to a novel massive phase characterized by a fractional magnetization plateau.
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