Ferromagnetism in the asymmetric Hubbard model

Andreas Mielke, Hal Tasaki

Wolfgang Nolting, Michael Potthoff, T. Herrmann +1 more

Grzegorz Górski, Jerzy Mizia, Krzysztof Kucab

We consider a Hubbard model with occupation dependent hopping integrals. Using the Hartree-Fock (H-F) approximation and the new Green function approach with inter-site kinetic averages included, we analyze the influence of the correlated hopping on ferromagnetic ordering. The influence of correlated hopping on the nonlocal quasiparticle energies and corresponding k-dependent spectral weights is included. In addition we obtain the shift of the spin bands which is a major factor in creating spontaneous ferromagnetism. At some parameters of the model the correlated hopping effect is strong enough to achieve saturated ferromagnetism. This state may be obtained at the asymmetric density of states (DOS) and the Fermi energy located in the region of large spectral weight near the band edge. The results are compared with DMFT-Quantum Monte Carlo calculations and with the Hubbard III approximation which includes the correlated hopping effect.

Grzegorz Górski, Jerzy Mizia, Krzysztof Kucab

We consider a Hubbard model (HM) with occupation dependent hopping integrals. Using the Hartree–Fock (H–F) approximation and the new Green's function approach with inter‐site kinetic averages included, we analyze the influence of the correlated hopping on ferromagnetic ordering. The influence of correlated hopping on the nonlocal quasiparticle energies and corresponding k‐dependent spectral weights is included. In addition, we obtain the shift of the spin bands, which is a major factor in creating spontaneous ferromagnetism. At some parameters of the model, the correlated hopping effect is strong enough to achieve saturated ferromagnetism. This state may be obtained at the asymmetric density of states (DOS) and the Fermi energy located in the region of large spectral weight near the band edge. The results are compared with DMFT‐Quantum Monte Carlo calculations and with the Hubbard III approximation, which includes the correlated hopping effect.

Robert Peters, Thomas Pruschke

We calculate the magnetic phase diagram of the Hubbard model for a Bethe lattice with nearest-neighbour (NN) hopping t 1 and next-nearest-neighbour (NNN) hopping t 2 in the limit of infinite coordination. We use the amplitude t 2 / t 1 of the NNN hopping to tune the density of states (DOS) of the non-interacting system from a situation with particle–hole symmetry to an asymmetric one with van-Hove singularities at the lower ( t 2 / t 1 >0) respectively upper ( t 2 / t 1 <0) band edge for large enough | t 2 / t 1 |. For this strongly asymmetric situation, we find rather extended parameter regions with ferromagnetic states and regions with antiferromagnetic states.

Ben Hur Bernhard