Effect of magnetic field on the spin resonance in FeTe0.5Se0.5 as seen via inelastic neutron scattering

Inelastic neutron scattering and susceptibility measurements have been performed on the optimally doped Fe-based superconductor FeTe0.5Se0.5, which has a critical temperature, T-c of 14 K. The magnetic scattering at the stripe antiferromagnetic wave vector Q=(0.5,0.5) exhibits a resonance at similar to 6 meV, where the scattering intensity increases abruptly when cooled below T-c. In a 7-T magnetic field parallel to the a-b plane, T-c is slightly reduced to similar to 12 K, based on susceptibility measurements. The resonance in the neutron-scattering measurements is also affected by the field. The resonance intensity under field cooling starts to rise at a lower temperature similar to 12 K, and the low-temperature intensity is also reduced from the zero-field value. Our results provide clear evidence for the intimate relationship between superconductivity and the resonance measured in magnetic excitations of Fe-based superconductors.