Spin-excitation anisotropy in the nematic state of detwinned FeSe

The origin of the electronic nematicity in FeSe is one most important unresolved puzzles study iron-based superconductors. In both spin- and orbital-nematic models, intrinsic magnetic excitations at Q1 = (1, 0) Q2 (0, 1) twin-free are expected to provide decisive criteria for clarifying this issue. Although a spin-fluctuation anisotropy below 10 meV between has been observed by inelastic neutron scattering low temperature, it remains unclear whether such an also persists higher energies associates with nematic transition Ts. Here we use resonant X-ray probe high-energy detwinned FeSe. A prominent along H K directions found persist E ≈ 200 meV, which decreases gradually increasing temperature finally vanishes around measured spin dispersive underdamped, can be understood from local-moment perspective.Taking together large energy scale far beyond dxz/dyz orbital splitting, suggest that probably spin-driven. mechanism drives behaviour superconductors still unclear. Now, shown disappear same indicating primarily