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

TL;DR

This paper investigates how ferromagnetic fluctuations near a critical point cause non-Fermi liquid behavior and Fermi surface quasi-splitting in two-dimensional electronic systems at low temperatures.

Contribution

It demonstrates the emergence of non-Fermi liquid self-energy and Fermi surface quasi-splitting due to ferromagnetic fluctuations, using multiple theoretical approaches.

Findings

Non-Fermi liquid self-energy form near the Fermi level

Two-peak spectral function structure at low temperatures

Fermi surface quasi-splitting in the paramagnetic phase

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 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.