1205.0425 (Raymond Fresard et al.)

Magnetic transitions in strong coupling expansions for nearly degenerate
states    [PDF]

Raymond Fresard, Christian Hackenberger, Thilo Kopp

We consider a strong coupling expansion for a two-band Hubbard model on two sites with nearly degenerate states. A comparative analysis is performed for different schemes of perturbation theory which are applicable to systems with nearly degenerate states. A fourth order approach which builds on a four-dimensional low-energy subspace with nearly degenerate states captures accurately the transition from an antiferromagnetic to a ferromagnetic ground state at large on-site Coulomb interaction.

View original: http://arxiv.org/abs/1205.0425