Abstract
Low-temperature heat capacity C(T) of the weakly electron-correlated SrNi2Ge2 122-layer compound undergoes a superconducting transition with onset at 1.4 K and a bulk T c =0.75 K, where heat-capacity jump ratio ΔC(T c )/γT c =0.88–1.05. A small average superconducting energy gap E g (ave)=2.21 kT c =0.14 meV is derived for this multi-gap superconductor. Similar results for isostructural SrPd2Ge2 include T c (onset)=3.5 K, bulk T c of 2.92 K, ΔC(T c )/γT c =0.70 and E g (ave)=2.54 kT c =0.64 meV. The higher T c onset could be associated with stoichiometric 1:2:2 grains in the polycrystalline samples. In addition, deviations of E g /kT c from the BCS ratio of 3.5 suggest that, just like their iron-based counterpart, these 122-layer germanides may also exhibit an unconventional, fully-opened multi-gap s-wave superconductivity.
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Acknowledgements
This work was supported by Grants No. NSC101-2112-M-007-013-009-MY3 and NSC100-2112-M-001-019-MY3 of the National Science Council of the Republic of China.
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J.C. Ho is visiting from Wichita State University, USA.
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Hung, T.L., Chen, I.A., Huang, C.H. et al. Low Temperature Heat Capacity of Layered Superconductors SrNi2Ge2 and SrPd2Ge2 . J Low Temp Phys 171, 148–155 (2013). https://doi.org/10.1007/s10909-012-0832-z
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DOI: https://doi.org/10.1007/s10909-012-0832-z