Ferromagnetism in the Hubbard model |
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Authors: | Andreas Mielke Hal Tasaki |
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Institution: | (1) Institut für Theoretische Physik, Universität Heidelberg, Philosophenweg 19, D-69120 Heidelberg, Germany;(2) Department of Physics, Gakushuin University, Mejiro, Toshima-ku, 171 Tokyo, Japan |
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Abstract: | Whether spin-independent Coulomb interaction can be the origin of a realistic ferromagnetism in an itinerant electron system has been an open problem for a long time. Here we study a class of Hubbard models on decorated lattices, which have a special property that the corresponding single-electron Schrödinger equation hasN
d-fold degenerate ground states. The degeneracyN
d is proportional to the total number of sites | |. We prove that the ground states of the models exhibit ferromagnetism when the electron filling factor is not more than and sufficiently close to =N
d/(2| |), and paramagnetism when the filling factor is sufficiently small. An important feature of the present work is that it provides examples of three dimensional itinerant electron systems which are proved to exhibit ferromagnetism in a finite range of the electron filling factor. |
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Keywords: | |
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