Nontrivial phonon dynamics and significant electron-phonon coupling of the high-frequency modes in a Dirac semimetal

Using finite temperature Raman spectroscopy, we investigate the electron-phonon interactions (EPI) and phonon-phonon scattering dynamics in the Dirac semimetal Cd3As2 in different frequency regimes. Strong softening of the Raman shifts below 200 K is observed for almost all the phonon modes with a marked deviation from the standard anharmonic behavior. The experimentally observed Raman linewidth seems to be captured well by a combination of EPI, relevant at low temperature (LT) and phonon-phonon scattering, which is predominant at high temperatures (HT), leading to an observable minima in the thermal evolution of the linewidth. While this feature is most prominently observed in the highest-frequency Raman mode (similar to 196 cm-1), its intensity gradually diminishes as the Raman frequency decreases. Computation of the electronic contribution to the phonon linewidth, for both the high and low frequency modes, from the phonon self-energy shows that it qualitatively mimics the experimental observations. It is found that phonon-induced interband scattering results in the presence of a maxima in phonon linewidth that crucially depends on the finiteness of the chemical potential.