Coulomb interactions and stability of the spiral states in the t-J model.

Abstract

A Schwinger-boson mean-field theory of the t-J model in the presence of Coulomb interactions is presented. It is shown that incommensurate spiral metallic states are favored over other important homogeneous states, and are stable against hole condensation for concentration \ensuremath{\delta}>${\mathrm{\ensuremath{\delta}}}_{\mathit{s}}$. For nearest-neighbor and screened-Coulomb potentials of reasonable strength the region of stability may coincide with the metallic phase of ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$. However, the instability always exists if \ensuremath{\delta} is small enough, a property which provides a mechanism for the occurrence of metal-insulator transition and antiferro- magetism in the low-\ensuremath{\delta} regime.