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| VOLUME 104 (2016) | ISSUE 12 | PAGE 864 |
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Direct Evidence of Two Superconducting Gaps in FeSe0.5Te0.5: SnS-Andreev Spectroscopy and Lower Critical Field
T. E. Kuzmichevaa, S. A. Kuzmicheva,b, A. V. Sadakova, A. V. Muratova, A. S. Usoltseva, V. P. Martovitskya, A. R. Shipilovb, D. A. Chareevc,d,e, E. S. Mitrofanovab, V. M. Pudalova
aP.N. Lebedev Physical Institute RAS, 119991 Moscow, Russia bM.V. Lomonosov Moscow State University, 119991 Moscow, Russia cInstitute of Experimental Mineralogy RAS, 142432 Chernogolovka, Russia dInstitute of Physics and Technology, Ural Federal University, 620002 Ekaterinburg, Russia eKazan Federal University, 420008 Kazan, Russia
Abstract
We present direct measurements of the superconducting order parameter in nearly optimal FeSe0.5Te0.5 single crystals with critical temperature  K. Using intrinsic multiple Andreev
reflection effect (IMARE) spectroscopy and measurements of lower critical
field, we directly determined two superconducting gaps,
 meV and  meV, and their temperature dependences.
We show that a two-band model fits well the experimental data. The estimated
electron-boson coupling constants
indicate a strong intraband and a moderate interband interaction.
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