Electronic and magnetic states in the two-band Hubbard model

L. B. Ioffe, A. I. Larkin

The two-dimensional Hubbard model is studied in the limit u/t\ensuremath{\gg}1. It is shown that almost all phase transitions are first-order transitions with a metastable-state lifetime depending discontinuously on the external parameters. The phase transition from the ferromagnetic to the ferrimagnetic state in a strong magnetic field is an exception: It is a second-order transition in a model with a half-filled electron band and it is a weakly-first-order transition in a model with a nearly-half-filled electron band. In the latter case the superconductive state is formed.

Thomas Maier, M. Zölfl, Thomas Pruschke +1 more

Oleg Derzhko, Mykola Maksymenko, Johannes Richter +2 more

We consider the one-orbital N -site repulsive Hubbard model on two kagome like chains, both of which yield a completely dispersionless (flat) one-electron band.Using exact many-electron ground states in the subspaces with n ≤ nmax (nmax ∝ N ) electrons, we calculate the square of the total spin in the ground state to discuss magnetic properties of the models.We have found that although for n < nmax the ground states contain fully polarized states, there is no finite region of electron densities n/N < 1 (N = N/3 or N = N/5) where ground-state ferromagnetism survives for N → ∞.

Hideki Matsumoto, Ferdinando Mancini

Takashi Yanagisawa, Izumi Hase, Mitake Miyazaki +1 more

We investigate the ground state of the two-dimensional single-band Hubbard model and three-band Hubbard model (d-p model) by using a variational Monte Carlo method. We employ an optimization variational Monte Carlo method. In this method the many-body wave function is improved and optimized by introducing variational parameters in the form: ψ = exp(- S ) ψ 0 where ψ 0 is a wave function, for example, the Gutzwiller function, and S is an operator used to include the many-body effect. The strong magnetic correlation is induced by the on-site Coulomb repulsive interaction U . The magnetic correlation plays a significant role in correlated electron systems as an origin of electron pairing as well as a main competitor of superconductivity. High-temperature superconductivity occurs in the strongly correlated region where U is greater than the bandwidth. We investigate the stability of antiferromagnetic state in the three-band d-p model.

Shiwei Zhang, Ettore Vitali, Adam Chiciak +1 more