Pressure-temperature phase diagrams of CaK(Fe1−xNix)4As4 superconductors

Abstract

The pressure dependence of the magnetic and superconducting transitions and that of the superconducting upper critical field are reported for CaK(Fe1−xNix)4As4, the first example of an Fe-based superconductor with spin-vortex-crystal-type magnetic ordering. Resistance measurements were performed on single crystals with two substitution levels (x=0.033,0.050) under hydrostatic pressures up to 5.12 GPa and in magnetic fields up to 9 T. Our results show that, for both compositions, magnetic transition temperatures TN are suppressed upon applying pressure; the superconducting transition temperatures Tc are suppressed by pressure as well, except for x=0.050 in the pressure region where TN and Tc cross. Furthermore, the pressure associated with the crossing of the TN and Tc lines also coincides with a minimum in the normalized slope of the superconducting upper critical field, consistent with a likely Fermi-surface reconstruction associated with the loss of magnetic ordering. Finally, at p∼4 GPa, both Ni-substituted CaK(Fe1−xNix)4As4 samples likely go through a half-collapsed-tetragonal phase transition, similar to the parent compound CaKFe4As4.

Source-reported materials — not catalogue approval

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