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The one-particle spectral weight of the two-dimensional Hubbard model is studied in the t -matrix approximation. A single quasi-particle peak is obtained in the spectrum so that the quasi-particle picture holds in the t -matrix approximation, while in the second-order perturbation (H. Fukuyama and M. Ogata: J. Phys. Soc. Jpn. 63 (1994) 3923) it is concluded that splitting of the spectral weight occurs.
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Narikiyo et al. (1995) studied this question.
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