Pressure-induced dependence of transport properties and lattice stability of CaK(Fe1–xNix)4As4

Here we report the investigation on correlation between the transport properties and the corresponding stability of the lattice structure for $\mathrm{CaK}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x})}_{4}{\mathrm{As}}_{4}$ ($x=0.04$ and 0), a new type of putative topological superconductors with and without a spin-vortex crystal (SVC) state in a wide pressure range involving superconducting (SC) to nonsuperconducting (NSC) transition and the half to full collapse of tetragonal [half-collapsed tetragonal (h-cT) and full-collapsed tetragonal (f-cT)] phases by the complementary measurements of high-pressure resistance, Hall coefficient, and synchrotron x-ray diffraction. The three critical pressures are identified: ${P}_{ch}^{\mathrm{on}}$ that is the turn-on critical pressure of the h-cT phase transition and it coincides with the critical pressure for the sign change of Hall coefficient from positive to negative, a manifestation of the Fermi surface reconstruction; ${P}_{ch}^{\mathrm{off}}$ that is the turn-off pressure of the h-cT phase transition; and ${P}_{cf}$ that is the critical pressure of the f-cT phase transition. By comparing the high-pressure results measured from the two kinds of samples, we find a distinct ``left-shift'' of the ${P}_{ch}^{\mathrm{on}}$ for the doped sample, at the pressure of which its SVC state is fully suppressed, however, the ${P}_{ch}^{\mathrm{off}}$ and the ${P}_{cf}$ remain the same as that of the undoped one. Our results not only provide a consistent understanding on the results reported before, but also demonstrate the importance of the Fe-As bonding in stabilizing the superconductivity of the iron pnictide superconductors through the ``pressure window.''