High-temperature superconductivity (Tc onset at 34 K) in the high-pressure orthorhombic phase of FeSe

We have studied the structural and superconducting properties of beta-FeSe under pressures up to 26 GPa using synchrotron radiation and diamond anvil cells. The bulk modulus of the tetragonal phase is 28.5(3) GPa, much smaller than the rest of Fe based superconductors. At 12 GPa we observe a phase transition from the tetragonal to an orthorhombic symmetry. The high-pressure orthorhombic phase has a higher T-c reaching 34 K at 22 GPa. Copyright (C) EPLA, 2009