Anisotropic resistivity in underdoped single crystals (Ba${}_{1-x}$K${}_x$)Fe${}_2$As${}_2$, $0\le x<0.35$

Abstract

Temperature-dependent in-plane, ${\rho }_a(T)$, and inter-plane, ${\rho }_c(T)$, resistivities were measured for the iron-arsenide superconductor (Ba${}_{1-x}$K${}_x$)Fe ${}_2$As${}_2$ over a broad doping range from parent compound to optimal doping $T_c\approx 38K$, $0\le x\le 0.35$. The coupled magnetic/structural transition at $T_{SM}$ is clearly observed for samples with $T_c<$26 K ($x<0.25$), however its effect on resistivity is much weaker than in the electron-doped Ba(Fe${}_{1-x}$Co${}_x$)Fe ${}_2$As${}_2$, and the transition leads only to a decrease of resistivity. In addition to the feature at $T_{SM}$, the inter-plane resistivity shows a maximum at $T^{\ast }\sim$200 K, which moves slightly to higher temperature with doping, revealing a trend opposite to the electron-doped materials. A smeared feature at about the same temperature is seen in ${\rho }_a(T)$. For $T<T^{\ast }$, the temperature dependence of resistivity shows systematic evolution and is close to linear at optimal doping. This feature, being most pronounced for ${\rho }_c(T)$, suggests the existence of a quantum critical point close to optimal doping.