Specific heat of the iron-based high-Tc superconductor SmO1-xFxFeAs

The specific heat C(T) of iron-based high-T-c superconductor SmO1-xFxFeAs (0 <= x <= 0.2) was systematically studied. For the undolied x = 0 sample, a specific heat jump was observed at 130 K. This is attributed to the structural or spin-density-wave transition, which also manifests on resistivity as a rapid drop. However, this jump disappears with slight F doping in the 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 LaO1-xFxFeAs. For the parent compound SmOFeAs, C(T) shows a sharp peak at 4.6 K, and with electron doping in the 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 Sm3+ ions in this system, which mimics the electron-doped high-T-c cuprate Sm2-xCexCuO4-delta.