Inhomogeneous superconductivity in thin crystals of FeSe1−xTex (x = 1.0, 0.95, and 0.9)

We investigated the temperature dependence of resistivity in thin crystals of FeSe _1−x Te _x (x = 1.0, 0.95, and 0.9), though bulk crystals with 1.0 ≧ × ≧ 0.9 are known to be non-superconducting. With decreasing thickness of the crystals, the resistivity of x = 0.95 and 0.9 decreases and reaches zero at a low temperature, which indicates a clear superconducting transition. The anomaly of resistivity related to the structural and magnetic transitions completely disappears in 55- to 155-nm-thick crystals of x = 0.9, resulting in metallic behavior in the normal state. Microbeam x-ray diffraction measurements were performed on bulk single crystals and thin crystals of FeSe _1−x Te _x . A significant difference of the lattice constant, c , was observed in FeSe _1−x Te _x , which varied with differing Te content (x), and even in crystals with the same x, which was mainly caused by inhomogeneity of the Se/Te distribution. It has been found that the characteristic temperatures causing the structural and magnetic transition ( T _t ), the superconducting transition ( T _c ), and the zero resistivity ( T _c ^zero ) are closely related to the value of c in thin crystals of FeSe _1−x Te _x .