Structure of the Order Parameter in Iron Pnictide-Based Superconducting Materials

Using data on the crystal symmetry of iron pnictides, we have calculated possible symmetries of singlet two-electron states corresponding to the superconducting order parameter. It has been shown that the octet line node structure observed in photoemission spectra is due to interaction between pairs of the same symmetry and that the presence of an odd component of a superconducting state in NMR spectra is associated with states on the Brillouin zone boundary.