Two-dimensional chiral stacking orders in quasi-one-dimensional charge density waves

TL;DR

This paper uncovers the existence of chiral stacking orders in quasi-one-dimensional charge density wave systems, revealing new forms of chirality and associated phenomena through microscopy, symmetry analysis, and theoretical calculations.

Contribution

It introduces the concept of two-dimensional chiral stacking orders in 1D CDW systems and identifies their relation to chiral winding numbers and topological features.

Findings

Discovery of three distinct chiral stacking orders: right-, left-, and nonchiral.

Identification of chiral winding numbers characterizing the stacking orders.

Observation of chiral vortices and domain walls linked to the stacking orders.

Abstract

Chirality manifests in various forms in nature. However, there is no evidence of the chirality in one-dimensional charge density wave (CDW) systems. Here, we have explored the chirality among quasi-one-dimensional CDW ground states with the aid of scanning tunneling microscopy, symmetry analysis, and density functional theory calculations. We discovered three distinct chiralities emerging in the form of two-dimensional chiral stacking orders composed of degenerate CDW ground states: right-, left-, and nonchiral stacking orders. Such chiral stacking orders correspond to newly introduced chiral winding numbers. Furthermore, we observed that these chiral stacking orders are intertwined with chiral vortices and chiral domain walls, which play a crucial role in engineering the chiral stacking orders. Our findings suggest that the unexpected chiral stacking orders can open a way to investigate the chirality in CDW systems, which can lead to diverse phenomena such as circular dichroism depending on chirality.