Specific heat of the iron-based high-$T_c$ superconductor SmO${}_{1-x}$F${}_x$FeAs

Abstract

The specific heat $C(T)$ of new iron-based high-$T_c$ superconductor SmO${}_{1-x}$F${}_x$FeAs ($0\le x\le 0.2$) was systematically studied. For undoped $x$ = 0 sample, a specific heat jump was observed at 130 K. This is attributed to the structural or spin-density-wave (SDW) transition, which also manifests on resistivity as a rapid drop. However, this jump disappears with slight F doping in $x$ = 0.05 sample, although the resistivity drop still exists. The specific heat $C/T$ shows clear anomaly near $T_c$ for $x$ = 0.15 and 0.20 superconducting samples. Such anomaly has been absent in LaO${}_{1-x}$F${}_x$FeAs. For the parent compound SmOFeAs, $C(T)$ shows a sharp peak at 4.6 K, and with electron doping in $x$ = 0.15 sample, this peak shifts to 3.7 K. It is interpreted that such a sharp peak results from the antiferromagnetic ordering of Sm${}^{3+}$ ions in this system, which mimics the electron-doped high-$T_c$ cuprate Sm${}_{2-x}$Ce${}_x$CuO${}_{4-\hat{I}´}$.

4 pages, 4 figures