Magnetic Measurements of Superconducting KxFe2-ySe2 Single Crystals Under High Pressure

Measurements of DC magnetization for single crystal specimens of KxFe2-ySe2 both under hydrostatic and uniaxial pressure have been performed using liquid Ar and NaCl as pressure transmitting media to generate hydrostatic and nearly uniaxial pressure, respectively. It has been found that TC is pressure independent below 2 GPa but decreases rapidly above 3 GPa under hydrostatic pressure, indicating that the bulk superconductivity disappears above 6 GPa. We have also observed a very weak diamagnetic response below ∽10 K for P≥6 GPa, suggesting that non-bulk superconductivity survives even under high pressure. On the other hand, TC is found to decrease rapidly above 1.5 GPa by the application of uniaxial pressure along c-axis, indicating that the lattice compression along c-axis suppresses the superconductivity more effectively. This suggests that c-axis lattice constant is an important factor to determine TC in KxFe2-ySe2.