Multiple-Q Instability by (d-2)-dimensional Connections of Fermi Surfaces

TL;DR

This paper introduces a universal mechanism for multiple-Q magnetic orderings driven by (d-2)-dimensional Fermi surface connections, applicable across various lattice structures, revealing a fundamental origin of complex spin textures.

Contribution

It identifies a universal Fermi surface instability mechanism based on (d-2)-dimensional connections, advancing understanding of multiple-Q orderings in itinerant magnets.

Findings

Instability driven by (d-2)-dimensional Fermi surface connections.

Universal fixed points in flow diagrams indicate robust instability.

Applicable to both frustrated and unfrustrated lattice systems.

Abstract

We propose a general mechanism of multiple-Q ordering with noncollinear and noncoplanar spin textures in itinerant magnets. By analyzing the fourth-order perturbation with respect to the spin-charge coupling, we find that the instability toward multiple-Q ordering is caused by (d-2)-dimensional connections of the Fermi surfaces in the extended Brillouin zone by the multiple-Q wave vectors: zero(one)-dimensional point (line) connections in the two(three)-dimensional systems. The instabilities are obtained as the "fixed points" in the two-parameter flow diagram, irrespective of lattice structures. The hidden Fermi surface instability provides a universal origin of noncollinear and noncoplanar instabilities common to frustrated and unfrustrated lattice systems.