Charge density waves in electron-doped molybdenum disulfide

TL;DR

This paper reports the first observation of a charge density wave in heavily electron-doped molybdenum disulfide, revealing unique CDW modulations linked to Fermi surface nesting and electron-phonon coupling, and offering new insights into CDW formation in TMDs.

Contribution

It demonstrates the existence of a CDW ground state in MoS₂ with distinct modulations, advancing understanding of CDW mechanisms in d² transition metal dichalcogenides.

Findings

Observation of a metal-insulator transition at 85 K

Identification of two CDW modulations: (2√3×2√3)R30° and 2×2

Linking CDW modulations to Fermi surface nesting and electron-phonon coupling

Abstract

We present the discovery of a charge density wave (CDW) ground state in heavily electron-doped molybdenum disulfide (MoS$_2$). This is the first observation of a CDW in any $d^2$ (column 6) transition metal dichalcogenide (TMD). The band structure of MoS$_2$ is distinct from the $d^0$ and $d^1$ TMDs in which CDWs have been previously observed, facilitating new insight into CDW formation. We demonstrate a metal-insulator transition at 85 K, a 25 meV gap at the Fermi level, and two distinct CDW modulations, $(2\sqrt{3}\times2\sqrt{3})$R$30^\circ$ and $2\times2$, attributable to Fermi surface nesting (FSN) and electron-phonon coupling (EPC), respectively. This simultaneous exhibition of FSN and EPC CDW modulations is unique among observations of CDW ground states, and we discuss this in the context of band folding. Our observations provide a route toward the resolution of controversies surrounding the origin of CDW modulations in TMDs.