Lattice dynamics of Dirac node-line semimetal ZrSiS

We report a comprehensive study of lattice dynamics of the Dirac node-line semimetal ZrSiS single crystal by Raman spectroscopy and first-principles calculations. The weak covalent bonding between ZrSiS layers is confirmed by the absence of low-frequency shear or breathing Raman modes down to $15\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$. All six Raman-active optical phonons are identified at 300 K, whose energies and symmetries match our phonon-dispersion calculations and polarized Raman measurements. The thermodynamic stability is verified from 77 to 300 K, and, with increasing temperature, sizable softening of Raman modes is observed with broadened profiles. The first-order temperature coefficients are found to be linearly dependent on temperature. Furthermore, using multiple excitation laser wavelengths of 488, 514.5, 568, 647, and 785 nm, we find that three out-of-plane Raman modes are all nondispersive, and their normalized intensity resonances at different laser energies can be attributed to the different interband transitions. Our work provides detailed information of ZrSiS lattice vibrations, as well as the coupling between ZrSiS lattice vibrations and its electronic states.