Laboratoire de Physique Théorique
Toulouse - UMR 5152

In this talk, I will present a recent application of the lattice functional renormalization group (FRG) to quantum XY spin models using a mapping to hardcore bosons. This mapping allows for the reinterpretation of the spontaneous magnetization in spin systems as the Bose condensation of magnons, and gives a natural framework to implement the lattice FRG. I will show how the FRG can take the hardcore constraint into account exactly, and will discuss the simplest approximation schemes. The results are in good agreement with Monte-Carlo simulations in two and three dimensions, and shows how the phase diagram can be reinterpreted at low densities using Bogoliubov theory.