Effect of controlled pointlike disorder induced by 2.5-MeV electron irradiation on the nematic resistivity anisotropy of hole-doped (Ba,K)Fe2As2

In-plane anisotropy of electrical resistivity was studied in samples of the hole-doped Ba1-xKxFe2As2 in the composition range 0.21 <= x <= 0.26 where anisotropy changes sign. Low-temperature (similar to 20 K) irradiation with relativistic 2.5 MeV electrons was used to control the level of disorder and residual resistivity of the samples. Modification of the stress-detwinning technique enabled measurements of the same samples before and after irradiation, leading to the conclusion of anisotropic character of predominantly inelastic scattering processes. Our main finding is that the resistivity anisotropy is of the same sign irrespective of residual resistivity, and remains the same in the orthorhombic C-2 phase above the reentrant tetragonal transition. Unusual T-linear dependence of the anisotropy Delta rho rho(a) (T ) - rho(b) (T) is found in pristine samples with x = 0.213 and x = 0.219, without similar signatures in either rho(a) (T ) or rho(b) (T ). We show that this feature can be reproduced by a phenomenological model of R. M. Fernandes et al. [Phys. Rev. Lett. 107, 217002 (2011)]. We speculate that onset of fluctuations of nematic order on approaching the instability towards the reentrant tetragonal phase contributes to this unusual dependence.