Internal and External Pressure Effects on Superconductivity in FeTe x Se 1-x (x = 0.46, 0.54) Single Crystals

We have synthesized and studied the transport properties of FeTe x Se 1-x (x = 0.4, 0.46, 0.5, 0.54, and 0.58) single crystals grown by slow cooling method and found a sharp increase of T c up to x = 0.46 followed by a moderate decrease of T c up to x = 0.58. We present the temperature dependence of electrical resistivity under various pressures up to ~ 2.5 GPa, and the pressure dependence of T c shows positive pressure coefficients of ~ 2.7 K/GPa and ~ 3.33 K/GPa for x = 0.46 and x = 0.54, respectively, up to 2 GPa followed by a decreasing trend with marginal variation of T c with negative pressure coefficients of − 0.602 K GPa −1 (x = 0.46) and − 0.7 K GPa −1 (x = 0.54) at maximum pressure of 2.5 GPa. Furthermore, both normal state resistivity and activation energy decrease sharply, and it suggests that the reduction of net electron-phonon scattering and densities of states (DOS) at the Fermi surface with application of pressure leads to enhancement of metallic behavior in FeSe systems.