Neutron Spin Resonance Near a Lifshitz Transition in Overdoped BaKFeAs
arXiv:2505.11000 · doi:10.1088/0256-307X/42/6/067405
Abstract
Elucidating the relationship between spin excitations and fermiology is essential for clarifying the pairing mechanism in iron-based superconductors (FeSCs). Here, we report inelastic neutron scattering results on the hole overdoped BaKFeAs near a Lifshitz transition, where the electron pocket at point is nearly replace by four hole pockets. In the normal state, the spin excitations are observed at incommensurate wave vectors with chimney-like dispersions. By cooling down to the superconducting state, a neutron spin resonance mode emerges with a peak energy of 14-15 meV weakly modulated along -direction. The incommensurability notably increases at low energies, giving rise to downward dispersions of the resonance mode. This behavior contrasts sharply with the upward dispersions of resonance observed in optimally doped BaKFeAs contributed by the hole to electron scattering, but resembles with the cases in KFeAs and KCaFeAsF where the fermiology are dominated by hole pockets. These results highlight the critical role of electronic structure modifications near the Fermi level, especially in governing interband scattering under imperfect nesting conditions, which fundamentally shape the spin dynamics of FeSCs.
7 pages, 4 figures, Accepted by Chinese Physics Letters as Express Letter
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