Giant Kohn anomaly and chiral phonons in the charge density wave phase of 1H-NbSe₂

2025/01/08 by Exists, Susy, Mardanya, Sougata, Markiewicz, Robert +6
#FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci) #Strongly Correlated Electrons (cond-mat.str-el)

paper · doi:10.48550/arxiv.2501.04821

Abstract

Despite extensive investigations, many aspects of charge density waves (CDWs) remain elusive, especially the relative roles of electron-phonon coupling and Fermi surface nesting as the underlying driving mechanisms responsible for the emergence of the CDW vector \bl Q_CDW. It is puzzling that even though electrons interact strongly with optical phonons in many correlated systems, the actual mode softening is of an acoustic mode. Here we consider monolayer 1H-NbSe₂ as an exemplar system, and through an accurate computation of the phonon self-energy, including its off-diagonal components. We provide compelling evidence that the relevant mode is a longitudinal optical phonon that softens by anti-crossing several intervening phonon bands. We also show that \bl Q_CDW is fixed by the convolution of the susceptibility and electron-phonon coupling, and that the softened phonons are circularly polarized.

Related

• Suppression of charge-density wave and superconductivity in a lithiated NbSe₂ monolayer
• Multiphonon interactions and collective excitations in charge density wave of transition metal dichalcogenides
• Lattice contribution to the unconventional charge density wave transition in 2H-NbSe₂: a non-equilibrium optical approach
• Revealing the Charge Density Wave caused by Peierls instability in two-dimensional NbSe₂
• Decisive role of electron-phonon coupling for phonon and electron instabilities in transition metal dichalcogenides