6 research outputs found
Multiband superconductivity and a deep gap minimum evidenced by specific heat in KCa(FeNi)AsF
Specific heat can explore low-energy quasiparticle excitations of
superconductors, so it is a powerful tool for bulk measurement on the
superconducting gap structure and pairing symmetry. Here, we report an in-depth
investigation on the specific heat of the multiband superconductors
KCa(FeNi)AsF ( = 0, 0.05, 0.13) single crystals
and the overdoped non-superconducting one with = 0.17. For the samples with
= 0 and = 0.05, the magnetic field induced specific heat coefficient
in the low temperature limit increases rapidly below 2 T,
then it rises slowly above 2 T. Using the non-superconducting sample with =
0.17 as a reference, and applying a mixed model that combines Debye and
Einstein modes, the specific heat of phonon background for various
superconducting samples can be fitted and the detailed information of the
electronic specific heat is obtained. Through comparative analyses, it is found
that the energy gap structure including two -wave gaps and an extended
-wave gap with large anisotropy can reasonably describe the electronic
specific heat data. According to these results, we suggest that at least one
anisotropic superconducting gap with a deep gap minimum should exist in this
multiband system. With the doping of Ni, the of the sample decreases
along with the decrease of the large -wave gap, but the extended -wave
gap increases due to the enlarged electron pockets via adding more electrons.
Despite these changes, the general properties of the gap structure remain
unchanged versus doping Ni. In addition, the calculation of condensation energy
of the parent and doped samples shows the rough consistency with the
correlation of with = 3-4, which is beyond the
understanding of the BCS theory