paper

Low temperature specific heat of the hole-doped Ba_{0.6}K_{0.4}Fe_2As_2 single crystals and electron-doped SmFeAsO_{0.9}F_{0.1} samples

arXiv:0812.1188 · doi:10.1103/PhysRevB.79.174501

Abstract

Low temperature specific heat (SH) was measured on the FeAs-based superconducting single crystals Ba $_{0.6}$ K $_{0.4}$ Fe $_{2}$ As $_{2}$ and high pressure synthesized polycrystalline samples SmFeAsO $_{0.9}$ F $_{0.1}$ . It is found that the sharp SH anomaly $I^ C / T ∣_{T_{c}}$ in Ba $_{0.6}$ K $_{0.4}$ Fe $_{2}$ As $_{2}$ reaches an unexpected high value of 98 mJ/mol K $^{2}$ , about one order of magnitude larger than that of SmFeAsO $_{0.9}$ F $_{0.1}$ ( $6 \sim 8$ mJ/mol K $^{2}$ ) samples, suggesting very high normal state quasiparticle density of states in FeAs-122 than in FeAs-1111. Furthermore, we found that the electronic SH coefficient $I^_{e}^{3} (T)$ of Ba $_{0.6}$ K $_{0.4}$ Fe $_{2}$ As $_{2}$ is weakly temperature dependent and increases almost linearly with the magnetic field in low temperature region, which may indicate that the hole-doped FeAs-122 system contains a dominant component with a full superconducting gap, although we cannot rule out the possibility of a small component with anisotropic or nodal gap. A detailed analysis reveals that the $I^_{e}^{3} (T)$ of Ba $_{0.6}$ K $_{0.4}$ Fe $_{2}$ As $_{2}$ cannot be fitted with a single gap of s-wave symmetry probably due to the multigap effect. These results indicate clear difference between the properties of the superconducting state of the holed-doped Ba $_{0.6}$ K $_{0.4}$ Fe $_{2}$ As $_{2}$ and the F-doped LnFeAsO (Ln = rare earth elements) systems, which we believe is originated from the complex Fermi surface structures in different systems.

9 pages, 10 figures