Observation of an Incommensurate Charge Density Wave in Monolayer TiSe_{2}/CuSe/Cu(111) Heterostructure

Area of Science:

• Condensed Matter Physics
• Materials Science
• Surface Science

Background:

• Titanium diselenide (TiSe2) is a layered material known for its charge density wave (CDW) properties.
• A commensurate CDW in bulk TiSe2 has a transition temperature of approximately 200 K.
• Incommensurate CDWs in bulk TiSe2 are of recent interest due to their link with superconductivity.

Purpose of the Study:

• To investigate the presence and nature of superstructures in monolayer TiSe2/CuSe/Cu(111) heterostructures.
• To characterize the observed superstructure and determine its relationship with charge density waves.
• To explore the influence of interface effects on CDW formation and properties.

Main Methods:

• Low-energy electron diffraction (LEED) for structural characterization.
• Scanning tunneling microscopy (STM) for real-space imaging of the superstructure.
• Analysis of wave vectors and band structure to identify the nature of the superstructure.

Main Results:

• Observation of an incommensurate superstructure in monolayer TiSe2/CuSe/Cu(111) heterostructures.
• Determination of the superstructure's main wave vector to be approximately 0.41a* or 0.59a*.
• Identification of the superstructure as an incommensurate charge density wave (I-CDW) with a transition temperature exceeding 600 K.
• Exclusion of moiré superlattices as the origin of the observed superstructure.

Conclusions:

• The monolayer TiSe2/CuSe/Cu(111) heterostructure hosts a robust I-CDW state.
• The I-CDW state exhibits a significantly higher transition temperature compared to the commensurate CDW in pristine TiSe2.
• Interface effects at the heterostructure are proposed to be crucial for the formation of this high-temperature I-CDW state.