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Collective modes in the paramagnetic phase of the Hubbard model

Abstract : The charge dynamical response function of the Hubbard model is investigated on the square lattice in the thermodynamic limit. The obtained charge-excitation spectra consist of a continuum, a gapless collective mode with anisotropic zero-sound velocity, and a correlation-induced high-frequency mode at ω≈U. The correlation function is calculated from Gaussian fluctuations around the paramagnetic saddle point within the Kotliar and Ruckenstein slave-boson representation. Its dependence on the on-site Coulomb repulsion U and density is studied in detail. An approximate analytical expression of the high-frequency mode, which holds for any lattice with one atom in the unit cell, is derived. Comparison with numerical simulations, perturbation theory, and the polarization potential theory is carried out. We also show that magnetic instabilities tend to vanish for T≳t/6, and finite-temperature phase diagrams are established.
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Contributor : Raymond Frésard Connect in order to contact the contributor
Submitted on : Friday, October 25, 2019 - 11:55:53 AM
Last modification on : Saturday, April 30, 2022 - 3:31:21 AM

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Vu Hung Dao, Raymond Fresard. Collective modes in the paramagnetic phase of the Hubbard model. Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2017, 95 (16), pp.336-342. ⟨10.1103/physrevb.95.165127⟩. ⟨hal-02333309⟩

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