Detailed magnetic and structural analysis mapping a robust magnetic C4 dome in Sr1-xNaxFe2As2

Abstract

The recently discovered $C_4$ tetragonal magnetic phase in hole-doped members of the iron-based superconductors provides new insights into the origin of unconventional superconductivity. Previously observed in Ba${}_{1-x}{A}_x$Fe${}_2$As${}_2$ (with $A=$ K, Na), the $C_4$ magnetic phase exists within the well studied $C_2$ spin-density wave (SDW) dome, arising just before the complete suppression of antiferromagnetic (AFM) order but after the onset of superconductivity. Here, we present detailed x-ray and neutron diffraction studies of Sr${}_{1-x}$Na${}_x$Fe${}_2$As${}_2$ ($0.10\le x\le 0.60$) to determine their structural evolution and the extent of the $C_4$ phase. Spanning $\Delta x\sim 0.14$ in composition, the $C_4$ phase is found to extend over a larger range of compositions, and to exhibit a significantly higher transition temperature, $T_r\sim 65$K, than in either of the other systems in which it has been observed. The onset of this phase is seen near a composition ($x\sim 0.30$) where the bonding angles of the Fe${}_2$As${}_2$ layers approach the perfect $109.46^{\circ }$ tetrahedral angle. We discuss the possible role of this return to a higher symmetry environment for the magnetic iron site in triggering the magnetic reorientation and the coupled re-entrance to the tetragonal structure. Finally, we present a new phase diagram, complete with the $C_4$ phase, and use its observation in a third hole-doped 122 system to suggest the universality of this phase.

arXiv comment14 pages, 10 figures, 2 tables

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• Local orthorhombicity in the magnetic $C_4$ phase of the hole-doped iron-arsenide superconductor Sr${}_{1-x}$Na${}_x$Fe${}_2$As${}_2$
• Coupling of structure to magnetic and superconducting orders in quasi-one-dimensional ${\text{K}}_2{\text{Cr}}_3{\text{As}}_3$
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• The breakdown of both strange metal and superconducting states at a pressure-induced quantum critical point in iron-pnictide superconductors
• Short-range nematic fluctuations in Sr1-xNaxFe2As2 superconductors
• Widespread orthorhombic fluctuations in the (Sr,Na)Fe${}_2$As${}_2$ family of superconductors
• Magnetic phase diagram of the iron pnictides in the presence of spin-orbit coupling: Frustration between $C_2$ and $C_4$ magnetic phases
• Intertwined spin-orbital coupled orders in the iron-based superconductors
• Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron Antiferromagnet Ca{1-x}Sr{x}Co{2-y}As{2}
• Phase Competition and Anomalous Thermal Evolution in High-Temperature Superconductors
• Large nematic susceptibility in the double-Q $C_4$ magnetic phase of Ba${}_{1-x}$Na${}_x$Fe${}_2$As${}_2$
• Strong Spin Resonance Mode associated with suppression of soft magnetic ordering in Hole-doped Ba1-xNaxFe2As2
• Preferred magnetic excitations in Sr${}_{1-x}$Na${}_x$Fe${}_2$As${}_2$
• Competition between orthorhombic and re-entrant tetragonal phases in underdoped Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ probed by the response to controlled disorder
• Soft elastic constants from phonon spectroscopy in hole-doped Ba${}_{1-x}$(K,Na)${}_x$Fe${}_2$As${}_2$ and Sr${}_{1-x}Na$_x$Fe$_2$As$_2$
• Optical and photoemission investigation of structural and magnetic transitions in the iron-based superconductor Sr${}_{0.67}$Na${}_{0.33}$Fe${}_2$As${}_2$
• Raman scattering study of tetragonal magnetic phase in Sr${}_{1-x}$Na${}_x$Fe${}_2$As${}_2$: structural symmetry and electronic gap
• Isostructural spin-density-wave and superconducting gap anisotropies in iron-arsenide superconductors
• Single-crystal growth of iron-based superconductor La${}_{0.34}$Na${}_{0.66}$Fe${}_2$As${}_2$
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