Pair spin dynamics in the spin 1/2 antiferromagnetic Heisenberg-Ising chain

We study pair spin dynamical structure factor of the spin-1/2 antiferromagnetic Heisenberg-Ising chain. Based on the Bethe ansatz formalism, various excitations at different energy scales are identified in the pair spin dynamics. With sum rules' guidance, we find that string excitations dominate the dynamical spectrum compared with low-energy fractional excitations. Our results establish a comprehensive picture for the pair spin dynamics, and will thus concretely facilitate measurements of relevant excitations in proper experimental setup.