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Phys. Rev. B 79, 020407(R) (2009) [4 pages]

Variational Monte Carlo study of ferromagnetism in the two-orbital Hubbard model on a square lattice

Katsunori Kubo
Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany and Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
Rapid Received 7 November 2008; revised 31 December 2008; published 27 January 2009

To understand the effects of orbital degeneracy on magnetism, in particular the effects of Hund's rule coupling, we study the two-orbital Hubbard model on a square lattice by a variational Monte Carlo method. As a variational wave function, we consider a Gutzwiller-projected wave function for a staggered spin- and/or orbital-ordered state. We find a ferromagnetic phase with staggered orbital order around quarter filling, i.e., electron number n=1 per site, and an antiferromagnetic phase without orbital order around half filling n=2. In addition, we find that another ferromagnetic phase without orbital order is realized in a wide filling region for large Hund's rule coupling. These two ferromagnetic states are metallic except for quarter filling. We show that orbital degeneracy and strong correlation effects stabilize the ferromagnetic states.

©2009 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevB.79.020407
DOI: 10.1103/PhysRevB.79.020407
PACS: 75.30.Kz; 71.10.Fd
  • 75.30.Kz
    Magnetic phase boundaries
  • 71.10.Fd
    Lattice fermion models (condensed matter)
  • YEAR: 2009
KEYWORDS: antiferromagnetism, ferromagnetism, Hubbard model, magnetic transitions, Monte Carlo methods, variational techniques, wave functions

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