Spectral Function for the S=1 Heisenberg Antiferromagetic Chain

We study the spectral function, $S(k,\omega )$ for the spin-1, one dimensional antiferromagnetic chain using a time-dependent density matrix renormalizaton group (DMRG) numerical method. We develop methods for extrapolating the time dependent correlation functions to larger times in order to enhance the frequency resolution. The resulting spectral functions are impressively precise and accurate. Our results confirm many qualitative expectations from non-linear $\sigma$ model methods and test them quantitatively. The critical wave-vector at which the single particle excitation emerges from the 2-particle continuum is estimated to be $0.23\pi -0.24\pi$.