Abstract
We present the discovery of a charge density wave (CDW) ground state in heavily electron-doped molybdenum disulfide (MoS2). This is the first observation of a CDW in any d2 (column 6) transition metal dichalcogenide (TMD). The band structure of MoS2 is distinct from the d0 and d1 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√3 × 2√3) R30° and 2 × 2, 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.
Highlights
We present the discovery of a charge density wave (CDW) ground state in heavily electron-doped molybdenum disulfide (MoS2)
Our observations provide a route toward the resolution of controversies surrounding the origin of CDW modulations in transition metal dichalcogenide (TMD)
CDWs are a periodic spatial oscillation of charge density, accompanied by a lattice distortion, that occur in crystalline materials due to electron−electron and electron−phonon interactions.[1−3] Despite intense investigation, the physics of CDW formation remains a topic of vigorous debate,[4,5] and the connection to other exotic electronic ground states, most notably superconductivity, remains controversial.[6]
Summary
We present the discovery of a charge density wave (CDW) ground state in heavily electron-doped molybdenum disulfide (MoS2). We notice that the apparent intensity of the 2 × 2 modulation varies within the image (Figure 2c), suggesting a nearly commensurate CDW phase, as observed in STM images of NbSe213 and copper-intercalated TiSe2.31 Examining again the Fourier transform of the larger area image, we see the 2 × 2 spots are faintly visible in this data.
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