Pressure-induced coevolution of transport properties and lattice stability in CaK(Fe1-xNix)4As4 (x= 0.04 and 0) superconductors with and without spin-vortex crystal state

TL;DR

This study explores how pressure affects the transport properties and lattice stability of CaK(Fe1-xNix)4As4 superconductors, revealing critical pressures where phase transitions and Fermi surface reconstructions occur, with implications for superconductivity stability.

Contribution

It provides the first detailed correlation between transport properties and lattice stability under pressure in CaK(Fe1-xNix)4As4, highlighting the role of Fe-As bonding in superconductivity.

Findings

Identification of three critical pressures P1, P2, P3 associated with phase transitions.

Observation of Fermi surface reconstruction at P1 coinciding with the onset of the h-cT phase.

Doping shifts P1 and suppresses the spin-vortex crystal state.

Abstract

Here we report the first investigation on correlation between the transport properties and the corresponding stability of the lattice structure for CaK(Fe1-xNix)4As4 (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 to non-superconducting transition and the half- to full-collapse of tetragonal (h-cT and f-cT) phases, by the complementary measurements of high-pressure resistance, Hall coefficient and synchrotron X-ray diffraction. We identify the three critical pressures, P1 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, P2 that is the turn-off pressures of the h-cT phase transition, and P3 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 P1 for the doped sample, at the pressure of which its SVC state is fully suppressed, however the P2 and the P3 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.