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Coexistence of Weak and Strong Coupling Mechanism, in an Iron-Based Superconductor FeSe 0.5 Te 0.5: Possible Signature of BCS-BEC Crossover

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Abstract

In this work, we present the scanning tunneling microscopy/spectroscopy (STM/STS) studies of an iron-based superconductor, F e S e 0.5 T e 0.5. 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/k B T c 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/E f ) of the material; which infers to the possible composite superconductivity in the realm of BCS-Bose Einstein Condensate (BEC) crossover.

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Acknowledgements

We would like to sincerely thank Prof. Vidya Madhavan from Boston College (currently at UIUC) for the valuable discussion. We would also like to acknowledge the support of the National Science and Technology Innovative Plan (NSTIP), Kingdom of Saudi Arabia, under the project 14-MAT362-04.

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Authors and Affiliations

  1. Department of Physics, King Fahd University of Petroleum and Minerals, Dhahran, 31261, Saudi Arabia

    S. Kunwar, R. M. Hamad & Kh. A. Ziq

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  1. S. Kunwar
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  2. R. M. Hamad
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  3. Kh. A. Ziq
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Correspondence to S. Kunwar.

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Kunwar, S., Hamad, R.M. & Ziq, K.A. Coexistence of Weak and Strong Coupling Mechanism, in an Iron-Based Superconductor FeSe 0.5 Te 0.5: Possible Signature of BCS-BEC Crossover. J Supercond Nov Magn 30, 3183–3188 (2017). https://doi.org/10.1007/s10948-017-4103-8

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