Q Dependence of Magnetic Resonance Mode on FeTe0.5Se0.5 Studied by Inelastic Neutron Scattering

Inelastic neutron scattering measurements have been performed on a superconducting single crystal FeTe0.5Se0.5 to examine the Q-dependent enhancement of the dynamical structure factor, S(Q,E), from Q = (0, 0) to (pi, pi), including (pi, 0) in the superconducting state. In most of iron-based superconductors, S(Q,E) is enhanced at Q = (pi, 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 = (pi, 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.