Band and momentum dependent electron dynamics in superconducting Ba(Fe1-xCox)2As2

We report results of electronic Raman scattering (ERS) experiments on high quality single crystals of Ba(Fe1-xCox)2As2 in the normal and superconducting states. With a light penetration depth of approximately 30 nm ERS is bulk sensitive. ERS highlights different regions in the Brillouin zone (BZ) for different combinations of the incoming and outgoing photon polarizations. Since the bands of the iron pnictides lie at high symmetry points in the BZ we can predominantly project out the hole (α) and electron (β) bands in A1g and B1g symmetry, respectively. We find a strong polarization dependence of the spectra which indicates band dependent carrier dynamics. In the superconducting state the presence of spectral weight down to the lowest accessible Raman shifts supports very small gaps. While true nodes with a sign change of the gap are unlikely, the spectra are compatible with accidental nodes, which may be lifted by doping and/or disorder. In the normal state we find Raman relaxation rates being almost constant and strongly temperature dependent on the α and β bands, respectively.