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Modern Physics Letters B

MAGNETIC PHASE DIAGRAM OF THE HUBBARD MODEL ON THE AB2 CHAIN

A. C. NASCIMENTO, André M. C. Souza

Published Aug 1, 2013• 0 citations
Publisher

Abstract

In this paper, a complete investigation of the magnetic properties of the Hubbard model on the AB2 chain is presented. We evaluate the magnetic phase diagram as a function of the electron–electron interaction and band filling by using the Green's function method within the Hartree–Fock approximation. Our results are in agreement with Lieb's theorem and the system shows ferromagnetic, ferrimagnetic, and paramagnetic phases.

DOI
10.1142/s0217984913501443

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We have studied the two-dimensional Hubbard model on a square lattice with nearest-neighbor hopping. We first discuss the properties of the model within the mean-field approximation: Because of the form of the band structure, some peculiar features are found. We then discuss the simulation algorithm used and compare simulation results with exact results for 6-site chains to test the reliability of the approach. We present results for thermodynamic properties and correlation functions for lattices up to 8\ifmmode\times\else\texttimes\fi{}8 in spatial size. The system is found to be an antiferromagnetic insulator for all values of the coupling constant at zero temperature in the half-filled-band case, but the long-range order is much smaller than predicted by mean-field theory. We perform a finite-size-scaling analysis to determine the character of the transition at zero coupling. For non-half-filled-band cases, our results suggest that the system is always paramagnetic, in contradiction with Hartree-Fock predictions. The system does not show tendency to ferromagnetism nor triplet superconductivity in the parameter range studied. We also discuss some properties of the attractive Hubbard model in the half-filled-band case.