Novel-ground-state properties of the two-dimensionalt?J model at low density

M. Yu. Kagan, Thomas Maurice Rice

Kazuhiro Sano, Ken'ichi Takano

Y. Ohta, Mina Murase, R. Eder +1 more

T. K. Lee, R. Eder, Y. C. Chen +3 more

C. Stephen Hellberg, Efstratios Manousakis

The phase diagram of the two-dimensional t-J model is determined accurately at low electron density by a combination of analytic and numerical techniques. The ground state exhibits three phases in the limit of zero electron density: an unpaired state at small J/t, a gas of s-wave pairs for 2J/t\ensuremath{\lesssim}3.4367, and a phase-separated state at larger interaction strengths. Bound states of larger clusters are never realized, and the instabilities present at small densities are discussed.

Liliana Arrachea

Using exact diagonalization techniques, the Hubbard model with hopping between nearest (t) and next-nearest neighbors ${(t}^{\ensuremath{'}})$ is studied in a two-dimensional cluster with $4\ifmmode\times\else\texttimes\fi{}4$ sites. Within a range of values of ${t}^{\ensuremath{'}}<0$ and low densities, states with different total spin are degenerate in the noninteracting system. At a finite value of the Coulomb repulsion U, states with high spin are energetically favored and the ground state can be fully polarized. The behavior of the density of states differs from that obtained within the Hartree-Fock approximation. The low energy region of the density of states (DOS) for the majority spins remains weakly modified by U. Our results bring further support to the idea that itinerant ferromagnetism occurs in strongly correlated systems with high noninteracting DOS at the bottom of the band.