Coherence effect in multiband superconductors: A suggestion of an experiment to determine the correct symmetry of the order parameter

An experimental method to determine the pairing symmetry in iron pnictides is theoretically proposed. We focus on two kinds of s-wave states, s _+-- and s₊₊-wave states, which are possible candidates for the pairing states of iron pnictides. For each state, we calculate both the density and spin response functions by using the two-band BCS model within the one-loop approximation. As a consequence, a clear difference is seen between the s_+-- and s₊₊-wave states in the temperature dependence of the response functions at nesting vector Q, which connects the hole and electron Fermi surfaces. We mention that this difference originates from the coherence effect in multiband superconductors. We suggest that the pairing symmetry could be identified by observing the temperature dependence of both the density and spin structure factors at low energies and at the nesting vector Q in neutron scattering measurements. Furthermore, we discuss the influence of impurities on the coherence effect in multiband superconductors.