Fermion Condensate as a New State of Matter

We demonstrate that in very many natural systems consisting of huge numbers of identical fermions at zero temperature a phase transition can happen that leads to a quite specific state called fermion condensate. As a signal of such fermion condensation quantum phase transition serves unlimited increase of the effective mass of quasi-particles that determine the excitation spectrum of multi-fermion system under consideration. We discuss the conditions, under which this transition happens, and illustrate the physical properties of a system that is located near this phase transition. The effective mass diverge when the inter-particle interaction is repulsive and medium strong as compared to particle's kinetic energy. So, low temperature and intermediate density plasma is a good candidate for such a phenomenon. Therefore, this paper can serve as a source of stimulating ideas when exploring a possible non-Fermi liquid behavior of plasma. A common and essential feature of such systems is a possibility to introduce quasiparticles that are different, however, from those suggested by L.D. Landau almost sixty years ago, by crucial dependence of temperature, external magnetic field, pressure and so on. These systems exhibit scaling behavior of their effective mass and other characteristics that are determined by this effective mass. It is demonstrated that a huge amount of experimental data on different strongly correlated compounds suggest that they, starting from some temperature and down, are governed by the fermion condensation quantum phase transition. ((c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)