Q dependence of magnetic resonance mode on FeTe_0.5Se_0.5 studied by inelastic neutron scattering

Inelastic neutron scattering measurements have been performed on a superconducting single crystal FeTe 0.5 Se 0.5 to examine the Q -dependent enhancement of the dynamical structure factor, S(Q,E), from Q = (0, 0) to (π, π), including (π, 0) in the superconducting state. In most of iron-based superconductors, S(Q,E) is enhanced at Q = (π, 0), where the ‘magnetic resonance mode’ is commonly observed in the unfolded Brillouin zone. Constant-E cuts of S(Q,E) suggest that the enhancement is not uniform in the magnetic excitation, and limited around Q = (π, 0). This result is consistent with the theoretical simulation of the magnetic resonance mode due to the Bardeen–Cooper–Schrieffer coherence factor with the sign-reversing order parameter of s ± wave.