Phase separation instabilities and magnetism in two dimensional square and honeycomb Hubbard model

Abstract

The variational cluster approximation is applied to rigorously calculate intrinsic local electron correlations in bipartite square and honeycomb Hubbard lattices. The Mott-Hubbard gap at half filling is manifested by a smooth metal-insulator transition in both lattices in agreement with the generic two-dimensional phase diagram. However, a density variation with the chemical potential shows the distinct structural differences away from half filling. The square lattice exhibits electron density discontinuity accompanied with spontaneous transition from antiferromagnetic Mott-Hubbard insulator into nonmagnetic metal. The spectral density anomaly and spin susceptibility peaks also are signaling on coexistence of hole rich metallic and hole poor insulating regions. In contrast, honeycomb lattice does not show density anomaly but displays a smooth transition with continuous evolution of homogenous metallic state. These calculations provide strong evidence for spontaneous phase separation instability found in our quantum cluster calculations at moderate U

Effects of correlations on honeycomb lattice in ionic-Hubbard model

“…The difference in occupation number can shows the phase transition of the system. The smooth shape of δn is according to results of [20]. Our calculations demonstrated the ∆n for large ∆ has fast change in 3 < U/t < 4 interval, for small energy gap and ∆ the occupation of each site has smooth variation.…”

“…[20], the variational cluster approximation (VCA) is applied to calculate local electron correlations in bipartite square and honeycomb lattices in Hubbard model, they found, in honeycomb lattice electron density displayed smooth metalinsulator transition with continuous evolution. The square lattice experienced metal-insulator transi-tion, but the electron density in square lattice displayed discontinuity with spontaneous transition [20]. The phase transition in the ionic Hubbard model has been investigated in a two-dimensional square lattice by determinant quantum Monte Carlo (DQMC).…”

Investigation of the residual stresses effect on the magnetic properties of CuO nanoparticles synthesized in a low-pressure arc discharge plasma

“…However, the appearance of defects and, as a consequence, the presence of excess charge carriers can lead to a fundamentally different fundamental feature, namely, the phase separation of the system and the appearance of polaron magnetic states in the antiferromagnetic (AF) matrix [2][3][4][5]. In this case, the orientation of each moment may change due to competing exchange interactions, for example, near defects in the anion and cation sublattices, or as a result of an incompletely filled coordination shell for surface ions.…”