Preferred Spin Excitations in the Bilayer Iron-Based Superconductor CaK(Fe$_{0.96}$Ni$_{0.04}$)$_4$As$_4$ with Spin-Vortex Crystal Order

Chang Liu; Philippe Bourges; Yvan Sidis; Tao Xie; Guanghong He; Frederic Bourdarot; Sergey Danilkin; Haranath Ghosh; Soumyadeep Ghosh; Xiaoyan Ma; Shiliang Li; Yuan Li; Huiqian Luo

doi:10.1103/PhysRevLett.128.137003

paper

Preferred Spin Excitations in the Bilayer Iron-Based Superconductor CaK(Fe $_{0.96}$ Ni $_{0.04}$ ) $_{4}$ As $_{4}$ with Spin-Vortex Crystal Order

arXiv:2202.11933 · doi:10.1103/PhysRevLett.128.137003

Abstract

The spin-orbit coupling (SOC) is a key to understand the magnetically driven superconductivity in iron-based superconductors, where both local and itinerant electrons are present and the orbital angular momentum is not completely quenched. Here, we report a neutron scattering study on the bilayer compound CaK(Fe $_{0.96}$ Ni $_{0.04}$ ) $_{4}$ As $_{4}$ with superconductivity coexisting with a non-collinear spin-vortex crystal magnetic order that preserves the tetragonal symmetry of Fe-Fe plane. In the superconducting state, two spin resonance modes with odd and even $L$ symmetries due to the bilayer coupling are found similar to the undoped compound CaKFe $_{4}$ As $_{4}$ but at lower energies. Polarization analysis reveals that the odd mode is $c -$ axis polarized, and the low-energy spin anisotropy can persist to the paramagnetic phase at high temperature, which closely resembles other systems with in-plane collinear and $c -$ axis biaxial magnetic orders. These results provide the missing piece of the puzzle on the SOC effect in iron-pnictide superconductors, and also establish a common picture of $c -$ axis preferred magnetic excitations below $T_{c}$ regardless of the details of magnetic pattern or lattice symmetry.

14 pages, 11 figures, including Supplementary Materials. Accepted for publication on Physical Review Letters

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Spin fluctuations in the 112-type iron-based superconductor Ca $_{0.82}$ La $_{0.18}$ Fe $_{0.96}$ Ni $_{0.04}$ As $_{2}$

Preferred Spin Excitations in the Bilayer Iron-Based Superconductor CaK(Fe0.96​Ni0.04​)4​As4​ with Spin-Vortex Crystal Order

Abstract

References in corpus (26)

Cited by in corpus (1)

Preferred Spin Excitations in the Bilayer Iron-Based Superconductor CaK(Fe $_{0.96}$ Ni $_{0.04}$ ) $_{4}$ As $_{4}$ with Spin-Vortex Crystal Order