Melting of Charge Density Waves in Low Dimensions

TL;DR

This paper investigates how charge density waves in low-dimensional materials undergo a continuous hexatic melting process, characterized by defect formation and observable through specific experimental signatures.

Contribution

It provides experimental evidence and explanation for the hexatic melting transition of incommensurate charge density waves in two-dimensional systems.

Findings

Observation of azimuthal superlattice peak broadening during melting

Detection of wavevector contraction as CDWs melt

Decay of integrated intensity indicating loss of CDW order

Abstract

Charge density waves (CDWs) are collective electronic states that can reshape and melt, even while confined within a rigid atomic crystal. In two dimensions, melting is predicted to be distinct, proceeding through partially ordered nematic and hexatic states that are neither liquid nor crystal. Here we measure and explain how continuous, hexatic melting of incommensurate CDWs occurs in low-dimensional materials. As a CDW is thermally excited, disorder emerges progressively$\unicode{x2013}$initially through smooth elastic deformations that modulate the local wavelength, and subsequently via the nucleation of topological defects. Experimentally, we track three hallmark signatures of CDW melting$\unicode{x2013}$azimuthal superlattice peak broadening, wavevector contraction, and integrated intensity decay.