Multigap Superconductivity and Strong Electron-Boson Coupling in Fe-Based Superconductors:A Point-Contact Andreev-Reflection Study of Ba(Fe_(1-x)Co_x)_2As_2 Single Crystals

摘要

Directional point-contact Andreev-reflection measurements in Ba(Fe_(1-x)Co_x)_2As_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 Ω_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 Ω_0 = 12 meV (=) Ω_b(0).