Europhys. Lett, 48 (5), pp. 561-567 (1999)
spl(2,1) dynamical supersymmetry and suppression of ferromagnetism in flat-band double-exchange models
K. Penc 1 and R. Lacaze 1,2
1 Service de Physique Théorique, CEA-Saclay -
91191 Gif-sur-Yvette Cedex, France
2 ASCI, Bât. 506, Université Paris Sud - 91405 Orsay Cedex, France
(received 28 April 1999; accepted in final form 30 September 1999)
PACS. 71.27+a - Strongly correlated electron systems; heavy fermions.
PACS. 75.30Mb - Valence fluctuation, Kondo lattice, and heavy-fermion phenomena.
PACS. 03.65Fd - Algebraic methods.
The low-energy spectrum of the ferromagnetic Kondo lattice model on an N-site complete graph extended with on-site repulsion is obtained from the underlying spl(2,1) algebra properties in the strong coupling limit. The ferromagnetic ground state is realized for 1 and N+1 electrons only. We identify the large density of states to be responsible for the suppression of the ferromagnetic state and argue that a similar situation is encountered in the Kagomé, pyrochlore, and other lattices with flat bands in their one-particle density of states.
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