Determinant Representations for Correlation Functions of Spin-1/2 XXX   and XXZ Heisenberg Magnets
  We consider correlation functions of the spin-$\half$ XXX and XXZ Heisenberg chains in a magnetic field. Starting from the algebraic Bethe Ansatz we derive representations for various correlation functions in terms of determinants of Fredholm integral operators. 
F.H.L. Essler, H. Frahm, A.G. Izergin, V.E. Korepin