Spin and Charge Susceptibilities in thed-pModel

Abstract

By including the higher order terms in the RPA in addition to the leading order terms of the 1/ N -expansion, the spin susceptibility χ s ( q ) and the charge susceptibility χ c ( q ) are investigated in the d - p model with the infinite on-site repulsion U d at the Cu-site and with the repulsion U p d between holes on the nearest-neighbor O- and Cu-sites. In this way the spin and charge fluctuations are taken into account on a common basis. In the low doping region, the antiferromagnetic order (AF) or the spin density wave (SDW) arises due to the nesting on the large Fermi surface in the in-gap state and the quasi-particle interaction at the low temperature. The enhancement of χ c due to U p d is found only in the over doping region, whereas in the leading order in the 1/ N -expansion it is found in the whole doping region.