Pressure shift of the zone-center TO mode of Zn

The pressure dependence of the transverse-optical zone-center phonon mode of Zn was measured by means of Raman spectroscopy up to 58 GPa at room temperature. The frequency increases under pressure and no anomaly is observed in the pressure range around 10 GPa where electronic topological transitions are expected to occur, and where also ab initio ``frozen phonon'' calculations predict a weak anomaly in the $c/a$ ratio. The relatively large value of the mode Gr\"uneisen parameter ${\ensuremath{\gamma}}_{i}=\ensuremath{-}d\mathrm{ln}{\ensuremath{\nu}}_{i}/d\mathrm{ln}V$ and its strong decrease under pressure are related to the high compressional anisotropy at ambient pressure and the gradual anisotropic $\ensuremath{\rightarrow}$ isotropic transition occurring with increasing pressure in Zn, respectively. An irregularity is observed in the pressure dependence of the line width around 10 GPa which may be related to changes in the phonon-phonon and electron-phonon interactions that could be a consequence of the electronic topological transitions.