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Article

Direct Evidence of Two Superconducting Gaps in FeSe_{0.5}Te_{0.5}: SnS-Andreev Spectroscopy and Lower Critical Field

JETP Letters. 2016. Vol. 104. No. 12. P. 864-864.
Pudalov V. M., Kuzmicheva T. E., Sadakov A. V., Muratov A. V., Usoltsev A. S., Martovitsky V. P., Shipilov A., Chareev D. A., Mitrofanova E. S.

We present direct measurements of the superconducting order parameter in nearly optimal FeSe Te single crystals with the critical temperature TC ≈ 14 K. Using the intrinsic multiple Andreev reflection effect (IMARE) spectroscopy and measurements of the lower critical field, we directly determined two superconducting gaps, ΔL ≈ 3.3−3.4 meV and ΔS ≈ 1 meV, and their temperature dependences. We show that a twoband model fits well the experimental data. The estimated electron–boson coupling constants indicate a strong intraband and a moderate interband interaction.