Magnetic fluctuations and self--energy effects in two--dimensional itinerant systems with van Hove singularity of electronic spectrum

TL;DR

This study uses functional renormalization group techniques to analyze magnetic fluctuations and self-energy effects in two-dimensional fermionic systems near van Hove singularities, revealing asymmetric magnetic behavior depending on the Fermi level position.

Contribution

It introduces a detailed analysis of magnetic fluctuations near van Hove singularities including self-energy corrections within a functional renormalization group framework.

Findings

Incommensurate magnetic fluctuations dominate above VHS.

Ferromagnetic ground state is indicated below VHS.

Magnetization follows a power-law dependence on magnetic field.

Abstract

We investigate a competition of tendencies towards ferromagnetic and incommensurate order in two-dimensional fermionic systems within functional renormalization group technique using temperature as a scale parameter. We assume that the Fermi surface (FS) is substantially curved, lies in the vicinity of van Hove singularity points and perform an account of the self-energy corrections. It is shown that the character of magnetic fluctuations is strongly asymmetric with respect to the Fermi level position relatively to van Hove singularity (VHS). For the Fermi level above VHS we find at low temperatures dominant incommensurate magnetic fluctuations, while below VHS level we find indications for ferromagnetic ground state. In agreement with the Mermin-Wagner theorem, at finite temperatures and in small magnetic fields we obtain rather small magnetization, which appears to be a power-law function of magnetic field. It is found that the FS curvature is slightly increased by correlation effects, and the renormalized bandwidth decreases at sufficiently low temperatures.