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Zeitschrift für Physik B Condensed Matter
ISSN: 0722-3277 (printed version)
ISSN: 1431-584X (electronic version)
Abstract Volume 103 Issue 2 (1997) pp 335-338
Mott-Hubbard transition and antiferromagnetism on the honeycomb lattice
L.M. Martelo (*), M. Dzierzawa, L. Siffert, D. Baeriswyl
Institut de Physique Théorique, Université de Fribourg, Pérolles, CH-1700 Fribourg, Switzerland
Abstract. The Hubbard model is investigated for a half-filled honeycomb lattice, using a variational method. Two trial wave functions are introduced, the Gutzwiller wave function, well suited for describing the "metallic" phase at small U and a complementary wave function for the insulating regime at large values of U. The comparison of the two variational ground states at the mean-field level yields a Mott transition at Uc/t \approx 5.3. In addition, a variational Monte Carlo calculation is performed in order to locate the instability of the "metallic" wave function with respect to antiferromagnetism. The critical value Um/t \approx 3.7 obtained in this way is considered to be a lower bound for the true critical point for antiferromagnetism, whereas there are good arguments that the mean-field value Uc/t \approx 5.3 represents an upper bound for the Mott transition. Therefore the "metal"rdquo;-insulator transition for the honeycomb lattice may indeed be simultaneously driven by the antiferromagnetic instability and the Mott phenomenon.
(*) Present address: Department of Physics, University of Évora, Apartado 94, P-7001 Évora Codex, Portugal
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