Observation of an Incommensurate Charge Density Wave in Monolayer TiSe2/CuSe /Cu (1 1 1 ) Heterostructure

TiSe₂ is a layered material exhibiting a commensurate (2 ×2 ×2 ) charge density wave (CDW) with a transition temperature of ∼2 0 0 K . Recently, incommensurate CDW in bulk TiSe₂ draws great interest due to its close relationship with the emergence of superconductivity. Here, we report an incommensurate superstructure in monolayer TiSe₂/CuSe /Cu (1 1 1 ) heterostructure. Characterizations by low-energy electron diffraction and scanning tunneling microscopy show that the main wave vector of the superstructure is ∼0.41 a^* or ∼0.59 a^* (here a^* is in-plane reciprocal lattice constant of TiSe₂ ). After ruling out the possibility of moiré superlattices, according to the correlation of the wave vectors of the superstructure and the large indirect band gap below the Fermi level, we propose that the incommensurate superstructure is associated with an incommensurate charge density wave (I-CDW). It is noteworthy that the I-CDW is robust with a transition temperature over 600 K, much higher than that of commensurate CDW in pristine TiSe₂ . Based on our data and analysis, we present that interface effect may play a key role in the formation of the I-CDW state.