Ferromagnetic instability in itinerant fcc lattice electron systems with higher order van Hove singularities: Functional renormalization group study

TL;DR

This study uses functional renormalization group analysis to explore ferromagnetic instability in an itinerant electron system on an fcc lattice with higher order van Hove singularities, revealing conditions for ferromagnetism and its suppression mechanisms.

Contribution

It introduces a detailed FRG approach to analyze ferromagnetic order near higher order van Hove singularities in the Hubbard model on an fcc lattice, highlighting the impact of density of states divergence.

Findings

Ferromagnetic order occurs near van Hove singularities with strong density of states divergence.

Curie temperature is significantly lower than RPA predictions due to interaction screening.

No strong tendency towards incommensurate order was observed away from singularities.

Abstract

We investigate the possibility of ferromagnetic ordering in the non-degenerate Hubbard model on the face-centered cubic lattice within the functional renormalization group technique using temperature as a scale parameter. We assume the relations between nearest, next-nearest, and next-next-nearest hopping parameters providing higher order (giant) van Hove singularity of the density of states. The ferromagnetic instability formation with lowering temperature is described consistently in the one-loop approximation for a one-particle irreducible vertex of two-particle electron interaction. The chemical potential versus temperature phase diagrams are calculated. We find ferromagnetic order only for sufficiently strong divergence of the density of states and fillings in the vicinity of van Hove singularity. The obtained Curie temperature is more than an order of magnitude smaller than the results of the random-phase approximation. The main origin of the suppression of ferromagnetism is the screening of interaction in the particle-particle channel. We also do not find the pronounced tendency towards incommensurate order when the Fermi level is moved away from a van Hove singularity, such that the first order quantum phase transitions from the ferro- to paramagnetic phase are obtained.