Abstract
Magnetism is widely considered to be a key ingredient of unconventional superconductivity. In contrast to cuprate high-temperature superconductors, antiferromagnetism in most Fe-based superconductors (FeSCs) is characterized by a pair of magnetic propagation vectors, (π,0) and (0,π). Consequently, three different types of magnetic order are possible. Of these, only stripe-type spin-density wave (SSDW) and spin-charge-density wave (SCDW) orders have been observed. A realization of the proposed spin-vortex crystal (SVC) order is noticeably absent. We report a magnetic phase consistent with the hedgehog variation of SVC order in Ni-doped and Co-doped CaKFe4As4 based on thermodynamic, transport, structural and local magnetic probes combined with symmetry analysis. The exotic SVC phase is stabilized by the reduced symmetry of the CaKFe4As4 structure. Our results suggest that the possible magnetic ground states in FeSCs have very similar energies, providing an enlarged configuration space for magnetic fluctuations to promote high-temperature superconductivity.
Highlights
Magnetic order and superconductivity seem intertwined and the ground-state can be tuned by pressure and doping
Magnetism in most Fe-based superconductors (FeSCs) [e.g., all AeFe2As2 (Ae = Ca, Sr, Ba)] is characterized by antiferromagnetic correlations with two symmetry-equivalent propagation vectors, Q1 = (π, 0) and Q2 = (0, π).[1,3]. Magnetic order with these propagation vectors can be described by the spatial variation of the iron magnetic moments at positions R, mðRÞ 1⁄4 M1 cos ðQ1 Á RÞ þ M2 cos ðQ2 Á RÞ: (1)
The Mössbauer spectra cannot be described by the moment motif of the spin-chargedensity wave (SCDW) phase where half the Fe-sites would experience Hhf = 0 (Fig. 1b)
Summary
The many families of Fe-based superconductors (FeSCs) provide a diverse platform for investigating the fundamental nature and applications of high-temperature superconductivity.[1,2] In these compounds, magnetic order and superconductivity seem intertwined and the ground-state can be tuned by pressure and doping. The many families of Fe-based superconductors (FeSCs) provide a diverse platform for investigating the fundamental nature and applications of high-temperature superconductivity.[1,2] In these compounds, magnetic order and superconductivity seem intertwined and the ground-state can be tuned by pressure and doping. Magnetism in most FeSCs [e.g., all AeFe2As2 (Ae = Ca, Sr, Ba)] is characterized by antiferromagnetic correlations with two symmetry-equivalent propagation vectors, Q1 = (π, 0) and Q2 = (0, π) (using the single-iron Brillouin zone notation).[1,3]. Magnetic order with these propagation vectors can be described by the spatial variation of the iron magnetic moments at positions R
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