Elastoresistance measurements on CaKFe_4As_4 and KCa_2Fe_4As_4F_2 with the Fe site of C_(2v) symmetry

摘要

We report resistance and elastoresistance measurements on (Ba_(0.5)K_(0.5))Fe_2As_2, CaKFe_4As_4, and KCa_2Fe_4As_4F_2. The Fe-site symmetry is D_(2d) in the first compound but C_(2v) in the latter two, which lifts the degeneracy of the Fe d_(xz) and d_(yz) orbitals. The temperature dependence of the resistance and elastoresistance is similar between the three compounds. Especially, the [110] elastoresistance is enhanced with decreasing temperature irrespective of the Fe-site symmetry. This appears to be in conflict with recent Raman scattering studies on CaKFe_4As_4, which suggest the absence of nematic fluctuations. We consider possible ways of reconciliation and suggest that the present result is important in elucidating the origin of in-plane resistivity anisotropy in iron-based superconductors.