We perform a finite-size analysis of the longitudinal and transverse structure factors
Sj(p,\ensuremath{\gamma},N),j=1,3 in the ground state of the one-dimensional spin-1/2 XXZ model. Comparison with the exact results of Tonegawa for the XX model yields excellent agreement.
We study the one-dimensional double-exchange model with L localized spins and one mobile electron. We solve the Schrödinger equation analytically and obtain the energies and wave functions for all the eigenstates with spin S = ( L − 1)***/2 exactly. As an application, we compute the single-particle Green's function. We show that, for vanishing exchange interactions between localized spins, the single-particle spectrum is entirely incoherent and the lowest band has an infinite band mass, i.e., the single electron is localized due to its interaction with the spin excitations. The analysis of the wave function gives us a particularly simple ground state.
The infinite-temperature space- and time-dependent spin-correlation functions
grx(t) are studied for the one-dimensional
XY model. Numerical calculations are performed to obtain the exact autocorrelation function
g0x(t) for chains containing 5, 7, and 9 spins (
S=21). This yields exact results for the first 16 moments of the frequency autocorrelation function of the infinite chain, and estimates for a few of the higher moments as well. The analysis suggests that
g0x(t) for the infinite chain is identical to $\frac{\mathrm{exp}(\ensuremath{-}{J}^{2}{t}^{2})}{4}$. We show that
grx(t) for $r\ensuremath{\ne}0$ vanishes identically for all values of time, implying a wave-vector-independent relaxation shape function. Our result for
g0x(t) is compared with that obtained by Huber for the classical ($S=\ensuremath{\infty}$) chain.