STM microscopy of the CDW in 1T-TiSe2 in the presence of single atom defects

TL;DR

This study uses STM and DFT to analyze the CDW in 1T-TiSe2 with single atom defects, finding the CDW remains largely unaffected and clarifying defect patterns and surface layer involvement.

Contribution

It provides detailed STM and DFT analysis showing the CDW in 1T-TiSe2 is resilient to native single atom defects and clarifies the defect structure and surface layer involvement.

Findings

No significant CDW modification by native defects

CDW modulation is in the Se surface layer

No 2H-polytype inclusions in the CDW phase

Abstract

We present a detailed low temperature scanning tunneling microscopy study of the commensurate charge density wave (CDW) in 1$T$-TiSe$_2$ in the presence of single atom defects. We find no significant modification of the CDW lattice in single crystals with native defects concentrations where some bulk probes already measure substantial reductions in the CDW phase transition signature. Systematic analysis of STM micrographs combined with density functional theory modelling of atomic defect patterns indicate that the observed CDW modulation lies in the Se surface layer. The defect patterns clearly show there are no 2$H$-polytype inclusions in the CDW phase, as previously found at room temperature [Titov A.N. et al, Phys. Sol. State 53, 1073 (2011). They further provide an alternative explanation for the chiral Friedel oscillations recently reported in this compound [J. Ishioka et al., Phys. Rev. B 84, 245125, (2011)].