THE PARAMAGNETIC SUSCEPTIBILITY AND CROSSOVER TRANSITION IN U=∞ HUBBARD MODEL

Abstract

Paramagnetic susceptibility χ(0, 0)=dR(H)/dH in (H→0, U=∞) Hubbard model has been calculated in the second order of a kinematic field. The final result changes cardinally the conclusion about paramagnetic’s instability which was derived from the theory of the first order in kinematic field at T=0 and ρ=1/2W.1 The obtained expression for χ(0, 0) possesses Pauli limit for n→0 with factor 2, has strong correlated enhancement (≈5 times as large) in the region of intermediate filling of the band (n≈0.5), and determines the paramagnetic-ferromagnetic transition as a crossover transition (i.e. without finite or infinite discontinuity).