Critical scaling of transport properties in the phase diagram of iron pnictide superconductors [formula omitted] and [formula omitted]

We present a systematic study of resistivity and thermoelectric power for iron pnictide systems [formula omitted] and [formula omitted] for [formula omitted]. Both systems show a similar phase diagram with an antiferromagnetic (AFM) phase on the low-doping side and a superconducting dome-shaped phase at higher doping. The AFM phase intersects the superconducting phase boundary. The extrapolation of the AFM phase boundary to zero temperature defines a critical doping of [formula omitted]. We show that the electrical and thermoelectric transport properties above the superconducting [formula omitted] obey a characteristic temperature scaling behavior at [formula omitted]. The crossover and scaling property indicates the existence of a (possibly hidden) magnetic quantum critical point in the phase diagram of the 122 iron pnictides. The results of this investigation prove the significance of magnetic fluctuations in iron pnictide superconductors.