Condensed Matter Physics, 2005, vol. 8, No. 4(44), p. 813-824, English
Entropy of fermionic models on highly frustrated lattices
(Technische Universität Braunschweig, Institut für
Theoretische Physik, Mendelssohnstrasse 3, 38106 Braunschweig,
(Institut für Theoretische Physik,
Otto-von-Guericke Universität Magdeburg, 39016 Magdeburg,
Spinless fermions on highly frustrated lattices are characterized
by the lowest single-particle band which is completely flat.
Concrete realizations are provided by the sawtooth chain
and the kagom\'e lattice. For these models a real-space picture
is given in terms of localized states. Furthermore, we find
a finite zero-temperature entropy for a suitable choice of the
chemical potential. The entropy is computed numerically at
finite temperature and one observes a strong cooling effect
during adiabatic changes of the chemical potential. We argue
that the localized states, the associated zero-temperature
entropy as well as the large temperature variations carry
over to the repulsive Hubbard model.
The relation to flat-band ferromagnetism is also discussed briefly.
flat band, localized states, frustrated lattice,
spinless fermions, Hubbard model, magnetocaloric effect
71.10.Fd, 65.40.Gr, 75.30.Sg, 75.10.Jm