and other transition metal dichalcogenides*

The underlying mechanism of charge density waves (CDW) is still an unresolved problem, both in general and in the specific scope of transition metal dichalcogenides (TMD). Here we report an Angle-Resolved Photoemission Spectroscopy (ARPES) study of the incommensurate CDW order in the 2H (trigonal prismatic) polytype of TaS₂. In this prototype two-dimensional system, we observed pronounced temperature independent, yet moment dependent many-body renormalizations of the electronic band dispersion. Detailed analysis revealed that these signatures can be related to phonon modes. Similar observations reported for TaSe₂ and NbSe₂ suggests this phononic origin can be a general phenomenon for TMDs. Furthermore, the persistence of these renormalizations was observed above CDW transition temperature corroborating pre-reported pseudogap effect. Also, the introduction of strong electron-phonon interactions to a tight binding model led to a successful explanation of a multitude of behaviors generally exhibited by CDW s in TMDs as well.