Non-Fermi-liquid behaviour and Fermi-surface expansion induced by van Hove-driven ferromagnetic fluctuations: the D-TRILEX analysis

TL;DR

This paper investigates how ferromagnetic fluctuations near a van Hove singularity in the Hubbard model lead to non-Fermi-liquid behavior and Fermi-surface expansion, using the advanced D-TRILEX method.

Contribution

It introduces a self-consistent D-TRILEX approach to analyze ferromagnetic fluctuations and their impact on electronic spectral functions and Fermi surface properties.

Findings

Spectral function splitting occurs at low temperatures.

Fermi surface area increases without splitting.

Non-Fermi-liquid excitations dominate near van Hove singularity.

Abstract

We consider the electronic and magnetic properties of the Hubbard model on a square lattice with the Fermi level near van Hove singularity and the ratio of the next-nearest-neighbor and nearest-neighbor hoppings $t'/t=-0.45$, which favours the ferromagnetic instability. We find, that a self-consistent consideration of the ferromagnetic fluctuations within the D-TRILEX approach results in the splitting of the electronic spectral function at low temperatures. This splitting exhibits only a weak momentum dependence, and only one of the split bands crosses the Fermi level. As a result, the Fermi surface itself remains unsplit, but its area increases, reflecting the presence of non-Fermi-liquid electronic excitations. We show that both the self-consistent account of the non-local contributions to the electronic self-energy and the proper treatment of electron interaction vertices in D-TRILEX are important to obtain this behaviour.