Time differential perturbed \(\gamma -\gamma\) angular correlation spectroscopy on \(^{111}\) Cd nuclei probes inserted into a high pressure-high temperature prepared \(\alpha\) - \(\hbox {Fe}_{1.01}\) Se compound was used to measure the electric-field gradients (EFG) at Fe and Se sites as a function of temperature. It is found that the EFGs at Fe and Se sites experience a local orthorhombic symmetry in the 100–300 K temperature range. With decreasing temperature, the asymmetry parameter \(\eta\) for \(^{111}\) Cd nuclei, located at the Fe sites, is found to grow from \(\eta \approx 0.5\) at \(T = 300\) K to \(\eta \approx 1\) at \(T = 90\) K, where the transition to the nematic phase sets in. This suggests that there are short-range orthorhombic fluctuations in FeSe even above the nematic transition temperature and complete braking of the axial symmetry at 90 K. Also, the EFG and asymmetry parameter were determined in the hexagonal \(\beta\) - \(\hbox {Fe}_{1.01}\) Se phase. The hyperfine quadrupole parameters were calculated using density functional theory (DFT) at the Fe and Se lattice sites for the tetragonal, orthorhombic and hexagonal phases of FeSe.
