Multigap Superconductivity and Strong Electron-Boson Coupling in Fe-Based Superconductors: A Point-Contact Andreev-Reflection Study of Ba(Fe1-xCox)2As2 Single Crystals

Directional point-contact Andreev-reflection measurements in Ba(Fe1-xCox)(2)As-2 single crystals (T-c = 24.5 K) indicate the presence of two superconducting gaps with no line nodes on the Fermi surface. The point-contact Andreev-reflection spectra also feature additional structures related to the electron-boson interaction, from which the characteristic boson energy Omega(b)(T) is obtained, very similar to the spin-resonance energy observed in neutron scattering experiments. Both the gaps and the additional structures can be reproduced within a three-band s +/- Eliashberg model by using an electron-boson spectral function peaked at Omega(0) = 12 meV similar or equal to Omega(b)(0).