Frank Göhmann: A quantum transfer matrix perspective on the XXZ chain

The exact calculation of measurable quantities for the integrable XXZ chain at finite temperature or under more general equilibrium conditions requires the use of the quantum transfer matrix and of the associated non-linear integral equations. We shall explain the construction and briefly review some of the known results for the correlation functions. Then we provide a closer look at two examples: The thermal form factor series for the two-point functions of spin-zero operators in the massive antiferromagnetic regime and in the zero-temperature limit, and the high-temperature asymptotic analysis of the transverse two-point functions of the XX chain at fixed finite time and distance.