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Journal of the Physical Society of Japan

Application of Cluster Variation Method to Three-Dimensionalt-JModel

Kazuyuki Tanaka, Yositake Takane, Hiromichi Ebisawa, Tohru Morita

Published Aug 15, 1994• 2 citations
Publisher

Abstract

The square approximation in the cluster variation method is formulated for the t - J model. By using this approximation, we study the phase transition to a magnetically ordered state in the three-dimensional t - J model on a cubic lattice. The Néel order is shown to appear near half-filled region.
DOI
10.1143/jpsj.63.2909

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We study the ground-state properties of the Hubbard model on the honeycomb lattice at half filling. Using the variational cluster approximation, We study the semimetal-insulator transition and antiferromagnetism as functions of the on-site Coulomb interaction U . When U is switched on, a small, but finite, single-particle gap appears; thus, we conclude that a tiny gap appears with arbitrary small U > 0. With further increases in U , the system goes into the antiferromagnetic state. We find that the staggered magnetization increases continuously with increasing U and that the antiferromagnetic phase transition is of the second order.