Preferred Spin Excitations in the Bilayer Iron-Based Superconductor CaK(Fe0.96Ni0.04)4As4 with Spin-Vortex Crystal Order
Chang Liu, Philippe Bourges, Yvan Sidis, Tao Xie, Guanghong He, Frédéric Bourdarot, Sergey Danilkin, Haranath Ghosh, Soumyadeep Ghosh, Xiaoyan Ma, Shiliang Li, Yuan Li, Huiqian Luo
DOI 10.1103/PhysRevLett.128.137003 · Physical Review Letters
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Abstract
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(Fe0.96Ni0.04)4As4 with superconductivity coexisting with a noncollinear spin-vortex crystal magnetic order that preserves the tetragonal symmetry of the 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 CaKFe4As4 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 Tc regardless of the details of magnetic pattern or lattice symmetry.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| CaK(Fe0.96Ni0.04)4As4 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 20.1 | Pressure not reported | unknown |
| CaKFe4As4 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 35 | Pressure not reported | unknown |
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