The specific heat coefficient Cp/T was investigated for the optimally doped Ba0.6K0.4Fe2As2 and Sr0.55K0.45Fe2As2. Previously, both the single- and the two-gap pairing have been suggested for Ba 0.6K0.4Fe2As2 single crystals. Our analysis reveals that the controversy is mainly caused by the differences in the adopted phonon background. This is especially true in the (Ba,K)Fe 2As2 system, in which the phonon contribution below 20 K significantly deviates from the simplified Debye model and, in addition, strongly depends on the doping. The different pairing features reported previously can be reproduced from the same Cp/T data set if the respective phonon baselines are adopted. The soft-phonon shifts, therefore, were examined on the (Ba,K)Fe2As2 and (Sr,K)Fe 2As2 systems, as well as the (Ba0.6K 0.4)(Fe,Co)2As2 system. The data show that although the K-Ba replacement may change the low-temperature slope β=dCp/Td(T2) by 50%, the effects of both K-Sr and Co-Fe replacements are much weaker. The carrier part, Ce/T, is consequently extracted for both Sr0.55K0.45Fe2As 2 and Ba0.6K0.4Fe2As2. The two-gap features appear in both cases, but the coupling strength is much stronger for the Ba-based superconductors.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2011 Aug 18|
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics