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Time-dependent Gutzwiller theory of magnetic excitations in the Hubbard model (Articolo in rivista)

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Time-dependent Gutzwiller theory of magnetic excitations in the Hubbard model (Articolo in rivista) (literal)

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Alternative label

G. Seibold (1); F. Becca (2); P. Rubin (3); J. Lorenzana (4) (2004)
Time-dependent Gutzwiller theory of magnetic excitations in the Hubbard model
in Physical review. B, Condensed matter and materials physics
(literal)

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(1) Institut für Physik, BTU Cottbus, P.O. Box 101344, 03013 Cottbus, Germany (2) INFM-Democritos, National Simulation Centre, and SISSA I-34014 Trieste, Italy (3) Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia (4) Center for Statistical Mechanics and Complexity, INFM, Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale Aldo Moro 2, 00185 Roma, Italy (literal)

Titolo

Time-dependent Gutzwiller theory of magnetic excitations in the Hubbard model (literal)

Abstract

We use a spin-rotational invariant Gutzwiller energy functional to compute random-phase-approximation-like (RPA) fluctuations on top of the Gutzwiller approximation (GA). The method can be viewed as an extension of the previously developed GA+RPA approach for the charge sector [G. Seibold and J. Lorenzana, Phys. Rev. Lett. 86, 2605 (2001)] with respect to the inclusion of the magnetic excitations. Unlike the charge case, no assumptions about the time evolution of the double occupancy are needed in this case. Interestingly, in a spin-rotational invariant system, we find the correct degeneracy between triplet excitations, showing the consistency of both computations. Since no restrictions are imposed on the symmetry of the underlying saddle-point solution, our approach is suitable for the evaluation of the magnetic susceptibility and dynamical structure factor in strongly correlated inhomogeneous systems. We present a detailed study of the quality of our approach by comparing with exact diagonalization results and show its much higher accuracy compared to the conventional Hartree-Fock+RPA theory. In infinite dimensions, where the GA becomes exact for the Gutzwiller variational energy, we evaluate ferromagnetic and antiferromagnetic instabilities from the transverse magnetic susceptibility. The resulting phase diagram is in complete agreement with previous variational computations. (literal)

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