Low-energy spin excitations in detwinned FeSe

Liu, R.*; Nakamura, Mitsutaka   ; Kamazawa, Kazuya*; Lu, X.*

Antiferromagnetic spin fluctuation is regarded as the leading driving force for electron pairing in high- superconductors. Here, we use inelastic neutron scattering (INS) to investigate the symmetry and in-plane wave-vector dependence of low-energy spin excitations in uniaxial-strain detwinned FeSe. The low-energy spin excitations ( 10 meV) appear mainly at = ( 1, 0) in the superconducting state ( 9 K) and the nematic state ( 90 K), confirming the constant C rotational symmetry and ruling out the C mode at 3 meV reported in a prior INS study. Moreover, our results reveal an isotropic spin resonance in the superconducting state, which is consistent with the wave pairing symmetry. At slightly higher energy, low-energy spin excitations become highly anisotropic.