Experimental evidence for a Bragg glass density wave phase in a transition-metal dichalcogenide

TL;DR

This study provides experimental evidence that the charge density wave in NbSe₂ exists in a Bragg glass phase, characterized by bound dislocation pairs and weak long-range effects despite strong local pinning by defects.

Contribution

The paper presents the first experimental indication of a Bragg glass phase in a transition-metal dichalcogenide, supported by STM data and Landau theory analysis.

Findings

Charge density wave in NbSe₂ is strongly pinned locally.

Dislocations occur in bound pairs, not freely.

Weak long-range effects of local modulation are observed.

Abstract

Analysis of the spatial dependence of current-voltage characteristics obtained from scanning tunneling microscopy experiments indicates that the charge density wave (CDW) occurring in NbSe$_2$ is subject to locally strong pinning by a non-negligible density of defects, but that on the length scales accessible in this experiment the material is in a "Bragg glass" phase where dislocations and anti-dislocations occur in bound pairs and free dislocations are not observed. A Landau theory-based analysis is presented showing how a strong local modulation may produce only a weak long range effect on the CDW phase.