Pressure-Induced Superconducting Phase with Structural Phase Transitions in EuSr₂Bi₂S₂Se₂F₄

We have reported the X-ray diffraction patterns and resistivity measurements of the BiS₂-based superconductor EuSr₂Bi₂S₂Se₂F₄ up to 15 GPa. High-pressure apparatuses include diamond anvil cells, piston cylinder cells, and cubic anvil cells. With applying pressure, peaks of T_c = 3.26 K (at 0.8 GPa) and T_c = 2.35 K (at 4 GPa) were observed by appear new superconducting phase. A new superconducting phase appeared owing to the structural phase transitions. At 7 GPa, superconductivity was not observed down to 2 K but above 8 GPa, superconductivity was observed near 3 K. Besides, we have also confirmed that superconductivity above 8.0 GPa also appeared with a structural phase transition (at 8.35 GPa). There are four types of superconducting phases below 12 GPa. Therefore, EuSr₂Bi₂S₂Se₂F₄ has complex superconducting phases, which can be attributed to the structural phase transitions.