Density-wave tendency from a topological nodal-line perspective

TL;DR

This paper introduces a novel perspective linking 2D spin density waves to 3D Dirac nodal-line systems under magnetic fields, revealing new insights into density wave mechanisms beyond traditional theories.

Contribution

It proposes a new mechanism connecting density waves to topological nodal-line structures, expanding the understanding of their origins beyond Fermi-surface nesting and electron-phonon interactions.

Findings

2D spin density-wave systems are equivalent to 3D Dirac nodal-line systems under magnetic fields.

The optimal wave vector varies continuously and is not directly related to original Fermi surfaces.

Numerical calculations support the proposed topological density wave mechanism.

Abstract

The understanding of density waves is a vital component of our insight into electronic quantum matters. Here, we propose an additional mosaic to the existing mechanisms such as Fermi-surface nesting, electron-phonon coupling, and exciton condensation. In particular, we find that certain 2D spin density-wave systems are equivalent to 3D Dirac nodal-line systems in the presence of a magnetic field, whose electronic structure takes the form of Dirac-fermion Landau levels and allows a straightforward analysis of its optimal filling. The subsequent minimum-energy wave vector varies over a continuous range and shows no direct connection to the original Fermi surfaces in 2D. Also, we carry out numerical calculations where the results on model examples support our theory. Our study points out that we have yet to attain a complete understanding of the emergent density wave formalism.