Anomalous Transport Properties and Phase Diagram of the FeAs-BasedSmFeAsO1−xFxSuperconductors

Abstract

We report the detailed phase diagram and anomalous transport properties of Fe-based high-$T_c$ superconductors ${\mathrm{SmFeAsO}}_{1-x}{\mathrm{F}}_x$. It is found that superconductivity emerges at $x\sim 0.07$, and optimal doping takes place in the $x\sim 0.20$ sample with the highest $T_c\sim 54\mathrm{K}$. $T_c$ 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 $x\sim 0.14$. 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: $\cot {\theta }_H\propto T^{1.5}$ for all samples with different $x$ in ${\mathrm{SmFeAsO}}_{1-x}{\mathrm{F}}_x$ system.