Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ferromagnetism in the Hubbard Model-- Examples from Models with
  Degenerate Single-Electron Ground States   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 Schr\"{o}dinger
equation has $N_{\rm d}$-fold degenerate ground states. The degeneracy $N_{\rm
d}$ is proportional to the total number of sites $\abs{\Lambda}$. We prove that
the ground states of the models exhibit ferromagnetism when the electron
filling factor is not more than and sufficiently close to $\rho_0=N_{\rm
d}/(2\abs{\Lambda})$, 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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The categories of this paper are: hep-ph
17
The categories of this paper are: q-fin
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The categories of this paper are: eess
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
34
The categories of this paper are: chem-ph
36
The categories of this paper are: cmp-lg
2
The categories of this paper are: math
7
The categories of this paper are: hep-th
6
The categories of this paper are: astro-ph
14
The categories of this paper are: math-ph
15
The categories of this paper are: nucl-ex
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The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org