  Charge density wave (CDW) is a periodic modulation of electronic charge
leading to a reconstruction of the lattice, an emergence of zone folded mode
along with collective excitations.1 Transition metal chalcogenides have shown a
great potential to study the underlying physics of multi body interactions like
electron-phonon (e-ph) as well as plasmons-phonon coupling,2,3 excitonic
complexes4 and CDW instabilities.5,6 We are elaborating on the collective
excitation and multiphonon interactions like amplitude, zone-folded and two
phonon (2_ph) mode associated with CDW in 2H-TaS2 and 2H-NbSe2. The 2_ph is a
unique excitation appears due to anharmonicity mediated longitudinal acoustic
modes associated with the Kohn anomaly and provides a substantial evidences of
e-ph coupling.7 The experimental observations of anomalous response of 2_ph
mode across CDW is clarified with phonon self-energy formalism. Transport
measurements shows that both materials exhibit incommensurate CDW (TI-CDW) at ~
76 K (2H-TaS2) and ~ 30 K (2H-NbSe2). As revealed by the estimated e-ph
coupling (l ~ 0.007 for 2H-NbSe2 and ~ 0.013 for 2H-TaS2) and anharmonicity
constant (d ~ 6.92 for 2H-NbSe2 and ~ 2.723 for 2H-TaS2), we emphasize on
higher e-ph coupling in 2H-TaS2 while larger anharmonicity 2H-NbSe2.
