  We calculate certain string correlation functions, originally introduced as
order parameters in integer spin chains, for the spin-1/2 XXZ Heisenberg chain
at zero temperature and in the thermodynamic limit. For small distances, we
obtain exact results from Bethe Ansatz and exact diagonalization, whereas in
the large-distance limit, field-theoretical arguments yield an asymptotic
algebraic decay. We also make contact with two-point spin-correlation functions
in the asymptotic limit.
