Dynamical correlations in an s=1/2 isotropic Heisenberg chain at T=

We present a study on the nature of the dynamical on-site spin-pair correlation in an s=1/2 isotropic Heisenberg chain at T= using the Mori-Lee formalism for solving the Heisenberg equation of motion and the direct summation method of evaluating infinite continued fractions. Our results are consistent with existing short-time analyses and support a power-law decay of the spin-pair correlations. Our study reveals that the frequency spectra corresponding to the on-site dynamical correlations can be seen as consisting of a Gaussian central peak presumably arising from the XY part of the Hamiltonian and a second broad finite frequency peak, which probably arises from the Ising part of the Hamiltonian and is slightly shifted toward a higher frequency than the Ising frequency.