Near-commensuration from Intertwined Charge Density Waves in Single-Layer TiSe₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid State Physics

Background:

• Charge density waves (CDWs) are fundamental electronic instabilities in solids.
• Near-commensurate (NC) states are predicted to form when CDW periods approach commensurate values.
• TiSe2 is a model system for CDW research, but its NC state has remained elusive.

Purpose of the Study:

• To image and characterize the elusive near-commensurate (NC) state in doped TiSe2 monolayers.
• To elucidate the nature of domain walls within the NC state.
• To investigate the coupling between CDWs and other electronic/structural modulations.

Main Methods:

• High-resolution imaging techniques (e.g., advanced microscopy) were employed.
• Detailed structural and electronic analysis was performed.
• Theoretical modeling was used to interpret the observed phenomena.

Main Results:

• A striking NC state was observed in ultraclean, doped TiSe2 monolayers.
• The domain walls were identified as sign-changing Ising-type walls of two coupled real CDWs, not complex CDW phase slips.
• An unexpected nematic modulation coupled to the CDWs was discovered.

Conclusions:

• TiSe2 exhibits a rare NC-CDW state involving two intertwined real modulations.
• The observed domain walls and nematicity offer new insights into CDW physics.
• This finding establishes TiSe2 as a unique platform for studying complex CDW phenomena.