Spin Excitations and Momentum Distributionin the Two-Dimensional Extended t-J Model

Abstract

The t^′ and t^{′ ′}-dependences of the dynamical spin correlation function S(q, , ω) of the 2D t-t^′-t^{′ ′}-J model are studied numerically based on the Lanczos algorithmfor two holes on 4 × 4 sites.In particular the spin excitations at q=( π, , π) ≡ q₀ are examined in detailand compared with results of the mean-field theory.The spin excitations turned out to be drastically different between YBCO(t^′=-0.17, t^{′ ′}=0.2) and YBCO(II)(t^′=-0.5, t^{′ ′}=0)-type, although both types reproduce the similar Fermisurfaces of YBCO and have the similar S(q₀, , ω) in themean-field theory.Further understanding of the properties of spin excitationfor these two choices of t^′ and t^{′ ′} are pursued by calculatingthe momentum distribution in the excited states.The spin excitations S(q₀, , ω) for YBCO(II)-typeare shown to be of collective type, while those for YBCO appear to be mainly individual.