We use polarized inelastic neutron scattering to study the spin-excitations anisotropy in the bilayer iron-based superconductor CaKFe4As4 (Tc = 35 K). In the superconducting state, both odd and even L−modulations of spin resonance have been observed in our previous unpolarized neutron scattering experiments (T. Xie {\it et al.} Phys. Rev. Lett. {\bf 120}, 267003 (2018)). Here we find that the high-energy even mode (∼18 meV) is isotropic in spin space, but the low-energy odd modes consist of a c−axis polarized mode around 9 meV along with another partially overlapped in-plane mode around 12 meV. We argue that such spin anisotropy is induced by the spin-orbit coupling in the spin-vortex-type fluctuations of this unique compound. The spin anisotropy is strongly affected by the superconductivity, where it is weak below 6 meV in the normal state and then transferred to higher energy and further enhanced in the odd mode of spin resonance below Tc.
@article{arxiv.2004.01405,
title = {Spin-Excitations Anisotropy in the Bilayer Iron-Based Superconductor CaKFe$_4$As$_4$},
author = {Tao Xie and Chang Liu and Frederic Bourdarot and Louis-Pierre Regnault and Shiliang Li and Huiqian Luo},
journal= {arXiv preprint arXiv:2004.01405},
year = {2020}
}
Comments
6 pages, 4 figures. Accepted by Physical Review Research