Understanding chiral charge-density wave by frozen chiral phonon

TL;DR

This paper investigates the microscopic origins of chiral charge-density waves using chiral phonons and electron-phonon coupling, proposing methods to engineer and detect chirality in CDWs, especially in 2D materials.

Contribution

It introduces a novel approach linking chiral phonons to chiral CDW transitions and suggests symmetry-breaking stimuli to control CDW chirality in experiments.

Findings

Chiral phonons influence the formation of chiral CDWs.

Anisotropy in Bragg peaks signals chiral CDW presence.

Symmetry-breaking stimuli can engineer CDW chirality.

Abstract

Charge density wave (CDW) is discovered within a wide interval in solids, however, its microscopic nature is still not transparent in most realistic materials, and the recently studied chiral ones with chiral structural distortion remain unclear. In this paper, we try to understand the driving forces of chiral CDW transition by chiral phonons from the electron-phonon coupling scenario. We use the prototypal monolayer 1T-TiSe$_2$ as a case study to unveil the absence of chirality in the CDW transition and propose a general approach, i.e., symmetry-breaking stimuli, to engineer the chirality of CDW in experiments. Inelastic scattering patterns are also studied as a benchmark of chiral CDW (CCDW, which breaks the mirror/inversion symmetry in 2D/3D systems). We notice that the anisotropy changing of Bragg peak profiles, which is contributed by the soft chiral phonons, can show a remarkable signature for CCDW. Our findings pave a path to understanding the CCDW from the chiral phonon perspective, especially in van der Waals materials, and provide a powerful way to manipulate the chirality of CDW.