Euclidean Gibbs Measures of Quantum Anharmonic Crystals

A lattice system of interacting temperature loops, which is used in the Euclidean approach to describe equilibrium thermodynamic properties of an infinite system of interacting quantum particles performing anharmonic oscillations (quantum anharmonic crystal), is considered. For this system, it is proven that: (a) the set of tempered Gibbs measures is non-void and weakly compact; (b) every Gibbs measure obeys an exponential integrability estimate, the same for all such measures; (c) every Gibbs measure has a Lebowitz-Presutti type support; (d) the set of all Gibbs measures is a singleton at high temperatures. In the case of attractive interaction and one-dimensional oscillations we prove that at low temperatures the system undergoes a phase transition. The uniqueness of Gibbs measures due to strong quantum effects (strong diffusivity) and at a nonzero external field are also proven in this case. Thereby, a complete description of the properties of the set of all Gibbs measures has been done, which essentially extends and refines the results obtained so far for models of this type.