Ruprecht-Karls-Universität Heidelberg
University of HeidelbergFaculty of Physics and AstronomyInstitut of Theoretical PhysicsAndreas MielkeAndreas Mielkeemail

Andreas Mielke
Institut for Theoretical Physics
Ruprecht-Karls University
Philosophenweg 19
D-69120 Heidelberg
Tel.: ++49 6221 549431 (Secretary)
Fax: ++49 6221 549331

Andreas Mielke: Ferromagnetism in the Hubbard model and Hund's rule
Phys. Lett. A174, 443-448 (1993) .


We investigate the Hubbard model with a $N_{\rm d}$-fold degenerate single particle ground state. If the number of electrons satisfies $N_{\rm e}<N_{\rm d}$, the model has ferromagnetic multiparticle ground states. We give a necessary and sufficient condition for the ground state to be unique $N_{\rm e}=N_{\rm d}$. It is ferromagnetic with spin $S=\frac12N_{\rm e}$. As a corollary, we obtain Hund's rule for the general Hubbard model with degenerate single particle eigenstates on translationally invariant lattices in the special case, where each of the degenerate single particle states if filled with one electron.


author="Andreas Mielke",
title="Ferromagnetism in the Hubbard model and Hund's rule",
journal="Phys. Lett. A",

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