Direct evidence of two superconducting gaps in FeSe0.5Te0.5: SnS-Andreev spectroscopy and the lower critical field

• Published in: JETP letters Vol. 104; no. 12; pp. 852 - 858
• Main Authors: Kuzmicheva, T. E., Kuzmichev, S. A., Sadakov, A. V., Muratov, A. V., Usoltsev, A. S., Martovitsky, V. P., Shipilov, A. R., Chareev, D. A., Mitrofanova, E. S., Pudalov, V. M.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.12.2016; Springer Nature B.V
• Subjects: Atomic; Biological and Medical Physics; Biophysics; Condensed Matter; Critical field (superconductivity); Critical temperature; Molecular; Optical and Plasma Physics; Order parameters; Particle and Nuclear Physics; Physics; Physics and Astronomy; Quantum Information Technology; Single crystals; Solid State Physics; Spintronics; Superconductivity
• ISSN: 0021-3640; 1090-6487
• DOI: 10.1134/S0021364016240048

We present direct measurements of the superconducting order parameter in nearly optimal FeSe Te single crystals with the critical temperature T C ≈ 14 K. Using the intrinsic multiple Andreev reflection effect (IMARE) spectroscopy and measurements of the lower critical field, we directly determined two superconducting gaps, Δ L ≈ 3.3−3.4 meV and Δ S ≈ 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.