Pressure-induced superconductivity in parent CaFeAsF single crystals

Flouroarsenide CaFeAsF is a parent compound of the 1111 type of iron-based superconductors. It is similar to the parent LaFeAsO, but it is oxygen-free. To date, studies of pressure-induced effects have only focused on pure and doped polycrystalline CaFeAsF samples. Here, we carried out high-pressure electrical resistivity and Hall coefficient measurements up to 48.2 GPa on single crystals of CaFeAsF. The structural transition temperature ${T}_{\mathrm{str}}$ decreased monotonically upon increasing the pressure, and reached $\ensuremath{\sim}60\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at 9.6 GPa. Superconductivity emerged suddenly at 8.6 GPa with the ${T}_{c,\mathrm{onset}}\ensuremath{\sim}25.7\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which decreased monotonically with increasing pressure to 5.7 K under 48.2 GPa. Moreover, just after the appearance of superconductivity, the Hall coefficient at 40 K started to decrease with increasing pressure, while keeping its sign negative persisting up to 48.2 GPa.