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TT: Tiefe Temperaturen

TT 15: Korrelierte Systeme I

TT 15.4: Talk

Thursday, March 20, 1997, 10:45–11:00, F1

Collective Spin Excitations in the 2D Hubbard Model — •R. Werner¹ and H. J. Schulz² — ¹Universit"at Dortmund, Institut f"ur Physik, D-44221 Dortmund — ²Université de Paris Sud, Laboratoire de Physique de Solides, F-91405 Orsay

Based on a functional integral approach a perturbative expansion of the partition function of the 2D Hubbard Hamiltonian is derived. A saddle point approximation is used to reproduce the mean field results. The wavevector dependence of the RPA magnetic susceptibility allows us to determine the wavevector distribution of the magnetic correlations yields incommensurate behavior at low temperatures. The incommensurate peak positions of the susceptibility agrees qualitatively with the neutron scattering results. A proper treatment of the vectorial order parameter allows an insight in the topological structure of the magnetic ordering. It is shown that the linear polarization of the ordering is energetically favorable. Three gapless Goldstone modes are found consisting of two transversal modes and a phase mode, all being degenerate in the low energy limit. Their dispersions, including the longitudinal optical branch, are calculated in the vicinity of the nesting vector.