Date of Original Version
New exact results are presented on the long-time asymptotic expansions of the T=0 autocorrelation functions, and on the leading singularities of their frequency-dependent Fourier transforms, for the one-dimensional S=1/2 isotropic XY model and the S=1/2 transverse Ising model at the critical field. High-precision numerical calculations of the latter functions are also given, and experiments are proposed to observe the functional behaviors that are found.
Gerhard Müller and Robert E. Shrock. Dynamic correlation functions for quantum spin chains. Phys. Rev. Lett. 51 (1983), 219-222. Available at: http://dx.doi.org/10.1103/PhysRevLett.51.219