Inhomogeneous superconductivity in thin crystals of FeSe_1-xTe_x (x = 1.0, 0.95, and 0.9)

We investigated the temperature dependence of resistivity in thin crystals of FeSe_1-xTe_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-xTe_x. A significant difference of the lattice constant, c, was observed in FeSe_1-xTe_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-xTe_x.