1998 Fiscal Year Final Research Report Summary
Theoretical Study on Quantum Phase Transition between Spin Liquid and Magnetic Order
| Project/Area Number |
09640417
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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 | University of Tsukuba |
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Principal Investigator |
TSUNETSUGU Hirokazu Univ.of Tsukuba, Inst.of Applied Physics, Associate Professor, 物理工学系, 助教授 (80197748)
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| Co-Investigator(Kenkyū-buntansha) |
SHIBATA Naokazu Univ.of Tsukuba, Inst.of Applied Physics, Research Associate, 物理工学系, 助手 (40302385)
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| Project Period (FY) |
1997 – 1998
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| Keywords | spin liquid / spin gap / antiferromagnetism / Kondo lattice / quantum phase transition / two-leg ladder lattice / electron coherence |
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| Research Abstract |
We have carried out theoretical investigations for the quantum phase transition between the spin-liquid and magnetically ordered phases. As well as the magnetic properties, effects on the charge dynamics have been studied. To this end, numerical calculations have been performed on three microscopic models : two-leg ladder system, the one-dimensional Kondo lattice, and the two-dimensional t-J model including additional electron-pair hopping processes.
To study the metallic spin-liquid phase, we have calculated the optical conductivity of the two-leg t-J ladder model at finite temperatures. The results show that its frequency dependence indicates an incoherent character similar to the two dimensional case at high temperatures. With decreasing temperature, an incoherent-to-coherent crossover takes place with accompanied by a pseudogap formation. This crossover is determined by the energy scale of the spin gap.
The electron dynamics in the two dimensions has been studied by calculating the D
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rude weight at zero temperature. The calculation was performed for the t-J model including electron-pair hopping processes. We have found that the conventional t-J model has the dynamic exponent, z=4, which dominates the incoherent dynamics observed near the metal- insulator transition. On the other hand, when the electron-pair hoppings are switched on, the dynamic exponent is z=2 and the electron dynamics recovers coherence.
The one-dimensional Kondo lattice model has been studied to see the critical behavior associated with hole doping for the spin-liquid state at half filling. Thermodynamics and local dynamic correlations have been calculated with the finite-temperature density-matrix renormalization-group method : We have found that the spin gap at half filling persists upon hole doping as the crossover energy scale dominating the local singlet formation. It is also found that a new energy scale appears in the lower energy region and it is determined by the energy scale of the Luttinger liquid ground state. Less
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