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

TL;DR

This study investigates how controlled electron irradiation affects the competition between orthorhombic and re-entrant tetragonal phases in underdoped Ba$_{1-x}$K$_x$Fe$_2$As$_2$, revealing phase-specific sensitivities to disorder.

Contribution

It provides new insights into the disorder response of competing magnetic phases in iron-based superconductors, highlighting the differential suppression rates of C_2 and C_4 phases.

Findings

Rapid suppression of the C_4 phase at 0.24 K/μΩ·cm at x=0.25.

Disorder stabilizes the C_2 phase while suppressing C_4.

Suppression rates differ from those in Ni-doped CaKFe$_4$As$_4$.

Abstract

Low-temperature (22~K) irradiation with 2.5~MeV electrons was used to study the competition between stripe ${\rm C_2}$ and tetragonal ${\rm C_4}$ antiferromagnetic phases which exist in a narrow doping range around $x=$0.25 in hole-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$. In nearby compositions outside of this range, at $x=$0.22 and $x=$0.19, the temperatures of both the concomitant orthorhombic/stripe antiferromagnetic transition $T_{\rm C2}$ and the superconducting transition $T_{\rm c}$ are monotonically suppressed by added disorder at similar rates of about 0.1~K/$\mu \Omega$cm, as revealed through using resistivity variation as an intrinsic measure of scattering rate. In a stark contrast, a rapid suppression of the ${\rm C_4}$ phase at the rate of 0.24 K/$\mu \Omega \cdot$cm is found at $x=$0.25. Moreover, this suppression of the ${\rm C_4}$ phase is accompanied by unusual disorder-induced stabilization of the ${\rm C_2}$ phase, determined by resistivity and specific heat measurements. The rate of the ${\rm C_4}$ phase suppression is notably higher than the suppression rate of the spin-vortex phase in the Ni-doped CaKFe$_4$As$_4$ (0.16 K/$\mu \Omega$cm).