Lowering of the spatial symmetry at theγ→αphase transition in cerium

Using time-differential perturbed angular correlation spectroscopy we have measured the electric field gradient (EFG) at $^{111}\text{C}\text{d}$ probe nuclei in solid Ce in a pressure range up to 8 GPa. Covering various allotropic phases of Ce, we find that the value of the EFG in the cubic $\ensuremath{\alpha}$ phase is almost four times larger than in the cubic $\ensuremath{\gamma}$ phase and close to values in the noncubic phases ${\ensuremath{\alpha}}^{\ensuremath{'}}$ and ${\ensuremath{\alpha}}^{\ensuremath{''}}$. These results together with the differences in time modulation of the spectra are interpreted as evidence for quadrupolar electronic charge-density ordering and symmetry lowering at the $\ensuremath{\gamma}\ensuremath{\rightarrow}\ensuremath{\alpha}$ transition while the lattice remains face-centered cubic.