Effect of Co doping on superconductivity and transport properties in SmFe${}_{1-x}$Co${}_x$AsO

Abstract

We investigate superconductivity and transport properties of Co doped SmFe${}_{1-x}$Co${}_x$AsO system. The antiferromagnetic (AFM) spin-density wave (SDW) order is rapidly suppressed by Co doping, and superconductivity emerges as $x$ $\ge$ 0.05. $T_c$${}^{mid}$ increases with increasing Co content, shows a maximum of 17.2 K at the optimally doping of $x\sim$ 0.10. A phase diagram is derived based on the transport measurements and a dome-like $T_c$ versus $x$ curve is established. Meanwhile we found that the normal state thermopower might consist of two different contributions. One contribution increases gradually with increasing $x$, and the other contribution is abnormally enhanced in the superconducting window 0.05 $\le$ $x$ $\le$ 0.20, and shows a dome-like doping dependence. A close correlation between $T_c$ and the abnormally enhanced term of thermopower is proposed.

5 pages, 5 figures; data added and text revised. A combined version (this paper and arXiv:0807.1304) published in PRB