Charge Order from Orbital-dependent Coupling Evidenced by NbSe$_2$

TL;DR

This paper demonstrates that the charge order in NbSe₂ arises from strong, momentum- and orbital-dependent electron-phonon coupling, providing a comprehensive explanation for experimental anomalies beyond weak-coupling theories.

Contribution

It introduces a model incorporating full momentum and orbital dependence of electron-phonon coupling, explaining charge order in NbSe₂ and similar materials beyond traditional weak-coupling approaches.

Findings

Strong electron-phonon coupling explains charge order in NbSe₂.

Momentum and orbital dependence are essential for accurate modeling.

Implications extend to other charge-ordered materials like cuprates.

Abstract

Niobium diselenide has long served as a prototype of two-dimensional charge ordering, believed to arise from an instability of the electronic structure analogous to the one-dimensional Peierls mechanism. Despite this, various anomalous properties have recently been identified experimentally which cannot be explained by Peierls-like weak-coupling theories. We consider instead a model with strong electron-phonon coupling, taking into account both the full momentum and orbital dependence of the coupling matrix elements. We show that both are necessary for a consistent description of the full range of experimental observations. We argue that NbSe$_2$ is typical in this sense, and that any charge-ordered material in more than one dimension will generically be shaped by the momentum and orbital dependence of its electron-phonon coupling as well as its electronic structure. The consequences will be observable in many charge-ordered materials, including cuprate superconductors.