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Spin-Dependent Mass Enhancement under Magnetic Field in the Periodic Anderson Model

In order to study the mechanism of the mass enhancement in heavy fermion compounds in the presence of magnetic field, we study the periodic Anderson model using the fluctuation exchange approximation. The resulting value of the mass enhancement factor z^{-1} can become up to 10, which is significantly larger than that in the single-band Hubbard model. We show that the difference between the magnitude of the mass enhancement factor of up spin (minority spin) electrons z^{-1}_up and that of down spin (majority spin) electrons z^{-1}_down increases by the applied magnetic field B//z, which is consistent with de Haas-van Alphen measurements for CeCoIn_5, CeRu_2Si_2 and CePd_2Si_2. We predict that z^{-1}_up >z^{-1}_down in many Ce compounds, whereas z^{-1}_up < z^{-1}_down in Yb compounds.