Nanoscale inhomogeneous superconductivity in Fe(Te_1-xSe_x) probed by nanostructure transport

Among iron-based superconductors, the layered iron chalcogenide Fe(Te_1-xSe_x) is structurally the simplest and has attracted considerable attention. It has been speculated from bulk studies that nanoscale inhomogeneous superconductivity may inherently exist in this system. However, this has not been directly observed from nanoscale transport measurements. In this work, through simple micromechanical exfoliation and high-precision low-energy ion milling thinning, we prepared Fe-(Te_0.5Se_0.5) nanoflakes with various thicknesses and systematically studied the correlation between the thickness and superconducting phase transition. Our result revealed a systematic thickness-dependent evolution of superconducting transition. When the thickness of the Fe(Te_0.5Se_0.5) flake is reduced to less than the characteristic inhomogeneity length (around 12 nm), both the superconducting current path and the metallicity of the normal state in Fe(Te_0.5Se_0.5) atomic sheets are suppressed. This observation provides the first transport evidence for the nanoscale inhomogeneous nature of superconductivity in Fe(Te_1-xSe_x).