Some Properties of Correlations of Quantum Lattice Systems in Thermal   Equilibrium
  Simple proofs of uniqueness of the thermodynamic limit of KMS states and of the decay of equilibrium correlations are presented for a large class of quantum lattice systems at high temperatures. New quantum correlation inequalities for general Heisenberg models are described. Finally, a simplified derivation of a general result on power-law decay of correlations in 2D quantum lattice systems with continuous symmetries is given, extending results of Mc Bryan and Spencer for the 2D classical XY model. 
Juerg Froehlich, Daniel Ueltschi
math-ph math.MP