Formation of Frustrated Charge Density Waves in Kagome Metal LuNb$_6$Sn$_6$

TL;DR

This study uncovers the formation of frustrated charge density waves in the kagome metal LuNb$_6$Sn$_6$, revealing precursor correlations, phonon softening, and the influence of Fermi surface topology on CDW behavior.

Contribution

It provides the first detailed experimental and theoretical analysis of CDWs in LuNb$_6$Sn$_6$, highlighting the role of lattice frustration and Fermi surface topology in CDW formation.

Findings

Observation of precursor CDW correlations with diffuse scattering patterns.

Detection of phonon softening near the CDW transition temperature.

Identification of frustrated CDW patterns with short phase coherence length.

Abstract

The charge density wave (CDW), a translational symmetry breaking electronic liquid, plays a pivotal role in correlated quantum materials, such as high-T$_c$ superconductors and topological semimetals. Recently, CDWs that possibly intertwine with superconductivity and magnetism are observed in various kagome metals. However, the nature of CDWs and the role of the Fermi surface (FS) topology in these materials remain an unresolved challenge. In this letter, we reveal the formation of CDWs in the newly discovered kagome metal LuNb$_6$Sn$_6$. We observe a precursor CDW correlation that features a "yield sign"-like hollow triangle diffuse scattering pattern and nearly complete softening of a flat optical phonon band near Q$_H$=(1/3, 1/3, 1/2). The scattering intensity of the precursor CDW displays divergent behavior as decreasing temperature until T$_{CDW}$=70 K, where a competing CDW at Q$_{CDW}$=(1/3, 1/3, 1/3) emerges. Using scanning tunneling microscopy/spectroscopy, we image the frustrated CDW patterns that show a short phase coherence length about ~20 nm in real space. Combined with first principles calculations, our observations support frustrated lattice interactions that are modulated by the FS topology. These results shed light on the interplay between FS and CDW in quantum materials with nearly degenerate structural deformation patterns.