Effects of pressure-induced phase transitions on superconductivity in single-crystal Fe 1.02 Se

The temperature dependence of the ac susceptibility for single-crystalline ${\text{Fe}}_{1.02}\text{Se}$ has been measured at high pressures to 6.7 GPa. The superconducting transition temperature ${T}_{c}$ displays a large increase from 7 to 30 K in the two-phase region at 0.5\char21{}1 GPa. Further increase in pressure results in the decrease in ${T}_{c}$ which drops below 4.2 K at 6.7 GPa.