Anomalous self-energy and Fermi surface quasi-splitting in the vicinity   of a ferromagnetic instability
  We discuss the low-temperature behavior of the electronic self-energy in the vicinity of a ferromagnetic instability in two dimensions within the two-particle self-consistent approximation, functional renormalization group and Ward-identity approaches. Although the long-range magnetic order is absent at T>0, the self-energy has a non-Fermi liquid form at low energies w<\Delta_0 near the Fermi level, where Delta_0 is the ground-state spin splitting. The spectral function at temperatures T<Delta_0 has a two-peak structure with finite spectral weight at the Fermi level. The simultaneous inclusion of self-energy and vertex corrections shows that the above results remain qualitatively unchanged down to very low temperatures T<<Delta_0. It is argued, that this form of the spectral functions implies the quasi-splitting of the Fermi surface in the paramagnetic phase in the presence of strong ferromagnetic fluctuations. 
A. A. Katanin (1,2), A. P. Kampf (3), and V. Yu. Irkhin (2) ((1)   Max-Planck-Institut fuer Festkoerperforschung, Stuttgart,...