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
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.