Integral representations for correlation functions of the XXZ chain at   finite temperature
  We derive a novel multiple integral representation for a generating function of the $\s^z$-$\s^z$ correlation functions of the spin-$\2$ XXZ chain at finite temperature and finite, longitudinal magnetic field. Our work combines algebraic Bethe ansatz techniques for the calculation of matrix elements with the quantum transfer matrix approach to thermodynamics. 
F. G\"ohmann, A. Kl\"umper and A. Seel