Strongly enhanced charge-density-wave order in monolayer NbSe2

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanoscience

Background:

• Two-dimensional (2D) materials exhibit distinct properties compared to their bulk forms.
• Many-body collective phenomena in 2D materials are less explored than single-particle electronic properties.

Purpose of the Study:

• Investigate the many-body collective-order phase diagram of niobium diselenide (NbSe2) down to the monolayer limit.
• Understand the impact of reduced dimensionality on charge density wave and superconducting phases.

Main Methods:

• Combined optical and electrical transport measurements.
• Fabrication and characterization of NbSe2 down to one monolayer thickness.

Main Results:

• Both charge density wave (CDW) and superconducting phases persist down to the monolayer limit.
• Superconducting transition temperature decreases with decreasing layer thickness.
• Charge density wave transition temperature significantly increases from 33 K in bulk to 145 K in monolayer NbSe2.
• Enhanced electron-phonon interactions in 2D NbSe2 drive the CDW enhancement, supported by observed blueshift in collective amplitude vibrations.

Conclusions:

• Atomically thin NbSe2 exhibits a remarkable enhancement of charge density waves.
• These findings expand the understanding of collective phenomena in 2D materials.
• The results suggest new avenues for controlling collective phases and developing novel electronic applications using 2D materials.