SPIN FLUCTUATIONS AND HOLON DYNAMICS IN THE LARGE-U HUBBARD-MODEL

The spin-holon effective Hamiltonian proposed by Zou and Anderson is used to calculate the chemical potential and the self-energy correction of spinons. Our results show that the effect of spin-exchange interaction is to enlarge the spinon bandwidth. For low temperatures and fixed doping fraction delta, the renormalized bandwidth and the chemical potential are nearly independent of temperature, but both change rapidly with the doping fraction. In the superfluid phase, the effect of increasing the doping fraction or increasing the on-site Coulomb repulsion U is to increase the relative kinetic energy of spinons, leading to a decrease in the superfluid transition temperature T(s)(delta), which is sensitive to various choices of U and the band parameter t; the increase in U tends to shift the boundary of T(s)(delta) towards a lower doping fraction. The correction due to spin fluctuations is extremely important for small doping fractions, leading to modification of the results of Baskaran, Zou and Anderson, and Ruckstein, Hirschfeld and Appel. Moreover, in the region of delta less-than-or-equal-to 8t/pi-2U, the effect of paramagnon fluctuations renders the mean-field theory invalid. We also discuss the effects of holon fluctuations on the mean-field results.