Raman spectroscopy of optical phonon and incommensurate charge density wave modes in 2H-TaSe2 exfoliated flakes

Abstract

2H-TaSe2 is a model transition metal dichalcogenide material that develops charge density waves (CDWs).Here we present variable-temperature Raman spectroscopy study on both incommensurate charge density waves (ICDW) and optical phonon modes of 2H-TaSe2 thin layers exfoliated onto SiO2 substrate. Raman scattering intensities of all modes reach a maximum when the sample thickness is about 11 nm. This phenomenon can be explained by optical interference effect between the sample and the substrate. The E2gICDW amplitude modes experience redshift as temperature increases. We extract ICDW transition temperature (TICDW) from temperature dependence of the frequency of E2gICDW mode. We find that TICDW increases in thinner flakes,which could be due to a result of significantly enhanced electron-phonon interactions. Our results open up a new window for search and control of CDW of two-dimensional matter.