| Budget Amount *help |
¥2,700,000 (Direct Cost : ¥2,700,000)
Fiscal Year 2003 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 2002 : ¥1,800,000 (Direct Cost : ¥1,800,000)
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| Research Abstract |
Charge gap in the Mott insulator originates from strong electron correlation. Therefore, we expect optical responses that are different from those in the band insulator. In. this project, we theoretically examine photoexcitaed states and nonlinear optical responses in insulating copper oxides that are typical Mott insulators by using a half filled Hubbard model and its effective model
We investigated the nonlinear optical responses in the two-dimensional Mott insulator, applying the numerically exact diagonalization technique to the effective model. We found that, in contrast to one dimension where spin and charge are separated, the interplay of photo-doped carriers and localized spins in the system plays a crucial role in the nonlinear optical responses. We also found that anomalous incident-photon energy dependence of the two-magonon Raman scattering in two-dimensional insulating cuprates is caused by the presence of the spins. In order to clarify the dependence of photoexcited states on dimensionality, we examined the temperature dependence of the linear optical absorption spectrum. In one-dimensional system, the there is no remarkable temperature dependence at low temperature because of spin-charge separation. In contrast, characteristic temperature dependences are found in two dimensions, which come from the interplay of carriers and spins. Not only the optically allowed but also forbidden states contributes in the nonlinear optical responses. To examine the distribution of both the states, we performed a dynamical density-matrix renormalization group calculation for the. one-dimensional Hubbard model. We found that the degeneracy of the states seen at large Coulomb interaction is lifted in real materials.
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