Anisotropic resistivity of Na$_{1-\delta}$Fe$_{1-x}$Co$_x$As

TL;DR

This study investigates the anisotropic resistivity in Na$_{1-eta}$Fe$_{1-x}$Co$_x$As, revealing doping-dependent electronic transport behaviors and crossover phenomena in a superconducting iron-arsenide compound.

Contribution

It provides detailed measurements of in-plane and out-of-plane resistivity in Co-doped NaFeAs, highlighting universal trends and crossover features related to doping and temperature.

Findings

Co doping stabilizes the compound and suppresses resistivity features.

In-plane resistivity shows a universal T-linear to T^2 evolution with doping.

Out-of-plane resistivity exhibits a non-monotonic temperature dependence with a doping-insensitive crossover at 80 K.

Abstract

Temperature-dependent resistivity is studied in single crystals of iron-arsenide superconductor Na$_{1-\delta}$Fe$_{1-x}$Co$_x$As for electrical current directions along, $\rho_a (T)$, and transverse, $\rho_c (T)$, to the Fe-As layers. Doping with Co increases stability of this compound to reaction with the environment and suppresses numerous features in both $\rho_a(T)$ and $\rho_c(T)$ compared to the stoichiometric NaFeAs. Evolution of $\rho_a (T)$ with $x$ follows a universal trend observed in other pnictide superconductors, exhibiting a $T$-linear temperature dependence close to the optimal doping and development of $T^2$ dependence upon further doping. $\rho_c (T)$ in parent compound shows a non - monotonic behavior with a crossover from non-metallic resistivity increase on cooling from room temperature down to $\sim$ 80 K to a metallic decrease below this temperature. Both $\rho_a (T)$ and $\rho_c (T)$ show several correlated crossover - like features at $T>$ 80 K. Despite a general trend towards more metallic behavior of inter - plane resistivity in Co-doped samples, the temperature of the crossover from insulating to metallic behavior (80 K) does not change much with doping.