Quasi-2D behavior of 112-type iron-based superconductors

Fluctuation magnetoconductivity and magnetization above the superconducting transition temperature (Tc) are measured on the recently discovered 112 family of iron-based superconductors (IBS), Ca${}_{1-x}$La${}_x$Fe${}_{1-y}$Ni${}_y$As${}_2$, which presents an extra As-As chain spacer-layer. The analysis in terms of a generalization of the Lawrence-Doniach (LD) approach to finite applied magnetic fields indicates that these compounds are among the most anisotropic IBS ($\gamma$ up to ~30), and provides a compelling evidence of a quasi-two-dimensional behavior for doping levels near the optimal one.