Superconductivity under Pressure in FeSe1-xTex Studied by DC Magnetic Measurements

Superconductivity under pressure in FeSe1-xTex with x= 0.7 (T-c similar to 14 K) has been investigated by the measurements of DC magnetization using high quality single crystal specimens. It has been found that T-c increases and makes a maximum of similar to 15 K at 1 GPa but rapidly decreases above 1 GPa under hydrostatic pressure using liquid Ar as pressure transmitting media (PTM). In contrast, T-c is found to increase up to 18 K at 2.5 GPa then decrease gradually under nearly uniaxial pressure along c-axis using NaCl as PTM. It is also found that T-c reaches a maximum of 16 K at 1 GPa but is nearly pressure independent above 1 GPa under nearly uniaxial pressure along a-axis. These behaviors suggest that the superconductivity is suppressed by the isotropic compression but is enhanced (not changed) by the uniaxial compression along c-axis (a-axis).