Dynamic correlations of antiferromagnetic spin-1/2 XXZ chains at arbitrary temperature from complete diagonalization

All eigenstates and eigenvalues are determined for the spin-1/2 XXZ chain H=2J Sigma(i)((SiSi+1x)-S-x+(SiSi+1y)-S-y+Delta (SiSi+1z)-S-z) for rings with up to N=16 spins, for anisotropies Delta=0, cos(0.3 pi), and 1. The dynamic spin pair correlations [S-l+n(mu)(t)S-l(mu)], (mu=x,z), the dynamic structure factors S-mu(q,omega), and the intermediate structure factors I-mu(q,t) are calculated for arbitrary temperature T. It is found that for all T, S-z(q,omega) is mainly concentrated on the region \omega\<epsilon(2)(q), where epsilon(2)(q) is the upper boundary of the two-spinon continuum, although excited states corresponding to a much broader frequency spectrum contribute. This is also true for the Haldane-Shastry model and the frustrated Heisenberg model. The intermediate structure factors I-mu(q,t) for Delta not equal 0 show exponential decay for high T and large q. Within the accessible time range, the time-dependent spin-correlation functions do not display the long-time signatures of spin diffusion.