Coupling to zone-center optical phonons in VSe2 enhanced by charge density waves

Abstract

We investigate electron-phonon coupling (EPC) in the charge density wave (CDW) phase of $\mathrm{V}{\mathrm{Se}}_{2}$ by Raman spectroscopy, angle-resolved photoemission spectroscopy (ARPES), and ab initio calculations. Zone folding induced by the $4\ifmmode\times\else\texttimes\fi{}4$ in-plane CDW phase promotes the appearance of a Raman peak at $\ensuremath{\sim}170\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. The suppression of ARPES intensity in parts of the Fermi surface is also a result of CDW-induced zone folding and anticrossing of the electron energy bands. The appearance of the new Raman peak is in line with the ARPES observation of a kink feature in the spectral function at the same energy. A self-energy analysis yields an EPC constant of $\ensuremath{\lambda}=0.3$. Our calculations of the EPC are in excellent agreement and reveal that the kink is caused by several optical phonon branches close in energy. Our paper highlights the CDW phase as a means of inducing EPC pathways to optical phonons that directly affect its Raman spectrum.