Non-linear canonical transformations and Kondo physics

We study the Kondo problem and the Kondo lattice using non-linear canonical transformations starting from the underlying Anderson model, generalizing the work of Ostlund in PRB 76, 153101 (2007). One such transformation, which is suitable to describe Fermi-liquid physics, provides an adiabatic connection between the quasi-particles of the interacting model and the electron- and hole-excitations in the non-interacting system as a function of the interaction parameter. We will also discuss other more unconventional transformations.