Resistivity, Hall effect, and magnetoresistance have been investigated systematically on single crystals of Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ ranging from undoped to optimally doped regions. A systematic evolution of these properties has been observed. It is found that the resistivity in the normal state of Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ is insensitive to the doped potassium concentration, which is very different from the electron-doped counterpart Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$, where the resistivity at 300 K reduces to the half value of the undoped one when the system is optimally doped. In stark contrast, the Hall coefficient R${}_H$ changes suddenly from a negative value in the undoped sample to a positive one with slight K doping, and it keeps lowering with further doping. We interpret this dichotomy as being due to the asymmetric scattering rate in the hole and the electron pockets with much higher mobility of the latter. The magnetoresistivity shows also a nonmonotonic doping dependence indicating an anomalous feature at about 80 to 100 K, even in the optimally doped sample, which is associated with a possible pseudogap effect. In the low-temperature region, it seems that the resistivity has similar values when superconductivity sets in, regardless of the different $T_c$ values, which indicates that the influence of impurity scattering on superconductivity is weak. A linear feature of resistivity ${\rho }_{ab}$ versus $T$ was observed just above $T_c$ for the optimally doped sample, suggesting a quantum criticality.

• Received 19 June 2011

DOI:https://doi.org/10.1103/PhysRevB.84.184512