Figure 1. Synchrotron high-energy x-ray diffraction and time-domain ⁵⁷Fe Mössbauer spectroscopy of FeSe under pressure.

(a,e–g) Show the evolution of the in-plane lattice parameters at various pressures determined from the splitting of the tetragonal (HH0) Bragg peaks. The colour corresponds to detector intensities integrated over the transverse scattering directions. (b) Shows a photograph of the content of the diamond anvil pressure cell used for these measurements including the FeSe single crystal, and ruby and silver pressure indicators. (c,d) Display the time-domain ⁵⁷Fe Mössbauer spectra at pressures P=2.5 and 4 GPa, respectively, with these data sets vertically offset for clarity. Grey lines are fits to the data.