Controlling the Charge Density Wave Transition in Single-Layer TiTe₂Se_2(1- Alloys by Band Gap Engineering

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid-State Chemistry

Background:

• Semiconductors with tunable band gaps offer routes to control collective electronic phases.
• Monolayer TiSe2 is a controversial material exhibiting charge density waves (CDWs).
• Engineering band gaps can influence excitonic insulator states.

Purpose of the Study:

• To explore band gap engineering in monolayer TiSe2 to achieve a semimetallic state.
• To investigate the evolution of CDW instability across the semiconductor-semimetal transition.
• To understand the microscopic mechanisms controlling collective states in 2D materials.

Main Methods:

• Molecular beam epitaxy for growing alloys of TiTe2Se2.
• In situ angle-resolved photoemission spectroscopy (ARPES) to study electronic structure.
• Model electronic structure calculations.

Main Results:

• Successful synthesis of monolayer TiTe2Se2 alloys across the full compositional range.
• Observation of the evolution of the (2 × 2) CDW instability through the semiconductor-semimetal transition.
• Identification of how band gap tuning affects excitonic and Peierls-like coupling.

Conclusions:

• Band gap engineering is a powerful method for controlling collective electronic states in 2D materials.
• Tuning the electronic structure of TiSe2 provides insights into CDW and excitonic insulator mechanisms.
• This approach offers a pathway to design novel quantum materials.