Charge Density Wave Order Driven By Momentum Dependent Electron-Phonon Coupling In 2H-TaS₂

Charge density waves (CDW) are exhibited by many low dimensional layered materials. However, when it comes to incommensurate CDW formation in transition metal dichalcogenides (TMD), the underlying microscopic mechanism is in controversy. Angle-resolved photoemission spectroscopy (ARPES) measurements on 2H-TaS₂ show that the CDW vector is not compatible with the pertinent Fermi surface nesting vectors, ruling out the textbook picture of Peierls like Fermi surface nesting as a candidate mechanism. Pronounced many-body renormalizations were observed in the electronic dispersion, which are manifested by the presence of multiple slope changes (`kinks’). The temperature independence of the kink energies implies that a strong electron-phonon coupling is present which was further observed to be momentum-dependent. The similar results gained on 2H-TaSe₂ and 2H- NbSe₂ rationalize the possible universality of the momentum-anisotropic strong electron-phonon coupling of incommensurate CDW order in 2H polytype of TMDs.