Abstract
In this work, we present the scanning tunneling microscopy/spectroscopy (STM/STS) studies of an iron-based superconductor, FeSe0.5Te0.5. We obtained differential conductance (dI/dV) spectra and extracted the value of the superconducting order parameter Δ using extended Bardeen Cooper Schieffer (BCS) phenomenology for anisotropic s-wave pairing. We observed widespread values of Δ from ∼0.6 to ∼4.5 meV, with distinct two peaks in the histogram around 1 and 3 meV. The corresponding values of 2Δ/kBTc for the peaks are ∼1.5 and ∼5.0, respectively, indicating coexistence of weak and strong coupling mechanism. We also found two different coupling mechanisms through Δ to Fermi energy ratio (Δ/Ef) of the material; which infers to the possible composite superconductivity in the realm of BCS-Bose Einstein Condensate (BEC) crossover.
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