Anomalous Transport Properties and Phase Diagram of the FeAs-Based SmFeAsO_1-xF_x Superconductors

We report the detailed phase diagram and anomalous transport properties of Fe-based high-T_c superconductors SmFeAsO_1-xF_x. It is found that superconductivity emerges at x∼0.07, and optimal doping takes place in the x∼0.20 sample with the highest T_c∼54  K. T_c increases monotonically with doping; the anomaly in resistivity from structural phase or spin-density-wave order is rapidly suppressed, suggesting a quantum critical point around x∼0.14. As manifestations, a linear temperature dependence of the resistivity shows up at high temperatures in the x<0.14 regime but at low temperatures just above T_c in the x>0.14 regime; a drop in carrier density evidenced by a pronounced rise in the Hall coefficient is observed below the temperature of the anomaly peak in resistivity. A scaling behavior is observed between the Hall angle and temperature: cot⁡θ_H∝T^1.5 for all samples with different x in SmFeAsO_1-xF_x system.