Spectral and structural signatures of phase transformation in the charge density wave material 1T−TaS2 intercalated with triethylenediamine

Abstract

Many transition-metal dichalcogenides show competing metallic, superconducting, charge density waves (CDWs), or Mott-insulating phases. Understanding the interplay between these phases is of fundamental interest. One approach to understand this relationship is to suppress one or more of the competing phases through systematic introduction of disorder. Intercalation is one of several approaches used to introduce this disorder. However, the intercalation process itself and the resulting changes in the atomic and electronic structure of the host-intercalant systems are not completely understood. Here, we characterize the structural and spectral signatures accompanying the intercalation of triethylenediamine [TED, (${\mathrm{C}}_{6}{\mathrm{H}}_{12}{\mathrm{N}}_{2}$)] into the CDW material $1T\text{\ensuremath{-}}\mathrm{Ta}{\mathrm{S}}_{2}$. Electron diffraction and electron microscopy imaging reveal that the intercalation of TED into $1T\text{\ensuremath{-}}\mathrm{Ta}{\mathrm{S}}_{2}$ leads to a change of the layer stacking in the intercalated $\mathrm{Ta}{\mathrm{S}}_{2}\text{\ensuremath{-}}\mathrm{TED}$ structure. Increased peak intensity is also observed between 3--5 eV in the valence electron-energy-loss spectra of the intercalated sample. Using electronic structure and theoretical spectra calculations we argue that these spectral features are a result of the band-structure changes due to structural phase transformation accompanying intercalation.