Intrinsic defects and perturbation of charge density waves (CDW) in 1T-TiSe₂

Charge density wave is an exciting quantum phenomenon. 1T-TiSe₂, a layered transition metal dichalcogenide (TMDC), undergoes a phase transition to a commensurate 2X2 CDW state below  T_CDW  ∽ 200 K. Excitonic condensation, Jahn-Teller mechanism, or both are contested mechanisms behind the second-order CDW phase transition in 1T-TiSe_2. Intrinsic defects like intercalation, substitution, or vacancies, introduced while growing the crystals, can be used to probe the nature of CDWs. We used scanning tunneling microscopy (STM) to study CDWs in the presence of Ti intercalation defect sites. STM images are used to measure the correlation length of CDWs. We observed a reduction in the correlation length of CDWs as Ti intercalation concentration increases. Ti intercalant causes the formation of small CDW-regions separated by domain boundaries. The electropositive nature of Ti intercalant leads to a change in carrier concentration, coloumb screening of electons and holes, affecting exciton condensate. This indicates that the excitonic condensation is the mechanism of the formation of the CDW state in 1T-TiSe_2.