Anomalous self-energy and Fermi surface quasisplitting in the vicinity of a ferromagnetic instability

Abstract

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 |ω| ≲ Δ 0 near the Fermi level, where Δ 0 is the ground-state spin splitting. The spectral function at temperatures T ≲ Δ 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 ≪ Δ 0. It is argued that this form of the spectral functions implies the quasisplitting of the Fermi surface in the paramagnetic phase in the presence of strong ferromagnetic fluctuations. © 2005 The American Physical Society.