Ferromagnetic fluctuations in the Rashba-Hubbard model

TL;DR

This paper investigates how ferromagnetic fluctuations emerge in the Rashba-Hubbard model due to band structure effects and spin-orbit coupling, highlighting their origin from interband contributions between electronlike and holelike Fermi surfaces.

Contribution

It reveals the specific conditions under which ferromagnetic fluctuations occur in the Rashba-Hubbard model, emphasizing the role of interband effects and Fermi surface topology changes.

Findings

Ferromagnetic fluctuations occur between two van Hove fillings.

Interband contributions drive ferromagnetic fluctuations.

Fermi surface topology change is linked to ferromagnetic behavior.

Abstract

We study the occurrence and the origin of ferromagnetic fluctuations in the longitudinal spin susceptibility of the $t$-$t'$-Rashba-Hubbard model on the square lattice. The combined effect of the second-neighbor hopping $t'$ and the spin-orbit coupling leads to ferromagnetic fluctuations in a broad filling region. The spin-orbit coupling splits the energy bands, leading to two van Hove fillings, where the sheets of the Fermi surface change their topology. Between these two van Hove fillings the model shows ferromagnetic fluctuations. We find that these ferromagnetic fluctuations originate from interband contributions to the spin susceptibility. These interband contributions only arise if there is one holelike and one electronlike Fermi surface, which is the case for fillings in between the two van Hove fillings. We discuss implications for experimental systems and propose a test on how to identify these types of ferromagnetic fluctuations in experiments.