Evidence of quantum criticality in the phase diagram of Kx Sr1-x Fe2 As2 from measurements of transport and thermoelectricity

The electrical transport and thermoelectric properties of Kx Sr1-x Fe2 As2 are investigated for 0≤x≤1. The resistivity ρ (T) shows a crossover from Fermi-liquid-like temperature dependence at small x to linear ∼T dependence at xc 0.4. With further increasing of x, (T) becomes nonlinear again. The thermoelectric power S (T) exhibits a similar crossover with increasing x with a logarithmic T dependence, S/T∼ln (T), near the critical doping xc. These results provide evidence for a quantum critical behavior due to the coupling of low-energy conduction electrons to two-dimensional spin fluctuations.