Engineering chiral density waves and topological band structures by multiple-$Q$ superpositions of collinear up-up-down-down orders

TL;DR

This paper demonstrates how multiple-Q superpositions of collinear up-up-down-down magnetic orders can stabilize chiral density waves and induce topologically nontrivial electronic structures, revealing new pathways to engineer magnetic and electronic properties.

Contribution

It introduces a theoretical framework showing the stabilization of multiple-Q UUDD states with chirality density waves in itinerant magnets, linking magnetic textures to topological electronic phases.

Findings

Stabilization of multiple-Q UUDD states with chirality density waves.

Induction of topological electronic structures such as Dirac semimetals and Chern insulators.

Observation of edge states dependent on chirality phase.

Abstract

Magnetic orders characterized by multiple ordering vectors harbor noncollinear and noncoplanar spin textures and can be a source of unusual electronic properties through the spin Berry phase mechanism. We theoretically show that such multiple-$Q$ states are stabilized in itinerant magnets in the form of superpositions of collinear up-up-down-down (UUDD) spin states, which accompany the density waves of vector and scalar chirality. The result is drawn by examining the ground state of the Kondo lattice model with classical localized moments, especially when the Fermi surface is tuned to be partially nested by the symmetry-related commensurate vectors. We unveil the instability toward the multiple-$Q$ UUDD states with chirality density waves, using the perturbative theory, variational calculations, and large-scale Langevin dynamics simulations. We also show that the chirality density waves can induce rich nontrivial topology of electronic structures, such as the massless Dirac semimetal, Chern insulator with quantized topological Hall response, and peculiar edge states which depend on the phase of chirality density waves at the edges.