Specific heat of the iron-based high-T_c superconductor SmO_1−xF_xFeAs

The specific heat C(T) of iron-based high-T_c superconductor SmO_1−xF_xFeAs (0x0.2) was systematically studied. For the undoped 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 LaO_1−xF_xFeAs. 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 Sm_2−xCe_xCuO₄₋.

©2008 The American Physical Society