Structural and electrical transport properties of Cu-doped Fe_1–x Cu _x Se single crystals*

We report the structural and electrical transport properties of Fe1–x Cu x Se (x = 0, 0.02, 0.05, 0.10) single crystals grown by a chemical vapor transport method. Substituting Cu for Fe suppresses both the nematicity and superconductivity of FeSe single crystal, and provokes a metal–insulator transition. Our Hall measurements show that the Cu substitution also changes an electron dominance at low temperature of un-doped FeSe to a hole dominance of Cu-doped Fe1–x Cu x Se at x = 0.02 and 0.1, and reduces the sign-change temperature (TR ) of the Hall coefficient (R H).