Quasiparticle Interference, quasiparticle interactions and the origin of the charge density-wave in 2H-NbSe$_{2}$

TL;DR

This study uses defect-enhanced quasiparticle interference imaging combined with ARPES data to reveal that charge density wave formation in 2H-NbSe2 is driven by quasiparticle interactions with phonons, not Fermi surface nesting.

Contribution

It introduces a method to analyze quasiparticle interference with intentionally introduced defects and combines it with ARPES to identify the origin of charge density waves.

Findings

Fermi surface nesting is not responsible for CDW in 2H-NbSe2.

Quasiparticle interactions with soft phonons drive the CDW formation.

Defect-enhanced quasiparticle interference reveals key electronic scattering processes.

Abstract

We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe$_{2}$, that we measure by scanning tunneling spectroscopic imaging. We show from the momentum and energy dependence of the quasiparticle interference that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe$_{2}$. We demonstrate that by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wavevector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiology and the interactions. In 2H-NbSe$_{2}$, we use this combination to show that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the CDW ordering wave vector.