One of the effective theories of significant success is that of Fermi liquids, formulated by L. V. Landau in the late 1950s and further developed by various authors, primarily from the Russian school [1, 2]. The fundamental idea is that a system of interacting particles can be described using a set of non-interacting quasi-particles. This concept is far from trivial. It is possible to add a particle to a collection of non-interacting quasi-particles, provided that the state of the new particle lies above the Fermi surface. In this case, the system remains stable.