High critical temperature superconductivity often occurs in systems where an antiferromagnetic order is brought near $T=0$ K by slightly modifying pressure or doping. ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$ is a superconducting, stoichiometric iron-pnictide compound showing optimal superconducting critical temperature with $T_c$ as large as 35 K. Doping with Ni induces a decrease in $T_c$ and the onset of spin-vortex crystal (SVC) antiferromagnetic order, which consists of spins pointing inwards to or outwards from alternating As sites on the diagonals of the in-plane square Fe lattice. Here we study the band structure of $\mathrm{CaK}{\left({\mathrm{Fe}}_{0.95}{\mathrm{Ni}}_{0.05}\right)}_4{\mathrm{As}}_4$ $(T_c=10 \mathrm{K},$ $T_{SVC}=50 \mathrm{K})$ using quasiparticle interference with a scanning tunneling microscope and show how the SVC modifies the band structure and induces a fourfold superconducting gap anisotropy.

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• Coherence length
• Spin fluctuations
• Superconducting order parameter
• Superconductivity
• Vortex lattices
• Iron-based superconductors
• Type-II superconductors
• Density functional theory
• Scanning tunneling spectroscopy