Noise spectroscopy of superconducting systems δ'-FeSe and FeSe0.5Te0.5

One of the most recent interesting and surprising phenomena is superconductivity in Fe-based compound (i.e. pnictides and chalcogenides), where FeSe has the most simple structure of the diverse family of these materials. The FeSe1-xTex system shows superconductivity up to Tc ∝ 14 K. The Fe planar structure may be crucial for understanding the mechanism of superconductivity in these systems: it was suggested that a low temperature structural distortion is closely associated with the superconducting properties of this material. We employ fluctuation (noise) spectroscopy to study the intrinsic charge carriers dynamics and their correlation with the structural properties. In both superconducting compounds δ'-FeSe and FeSe0.5Te0.5 we observe a maximum in the normalized noise power spectral density at 107 K and 110 K respectively, where a structural transition from tetragonal to orthorhombic occurs.