A detailed quantitative study of the pnictide composite superconductor (CS) Ba0.6K0.4Fe2As2 is presented in the frame-work of the recently derived set of generalized BCS equations. Invoking multiple Debye temperatures to take into account anisotropy of the CS, we address the current experimental data on its Tc and the (not so clear-cut) gap-values via different theoretical scenarios that attempt to identify the ion species responsible for pairing in it. This is done with the aid of the Bogoliubov’s restriction on the BCS dimensionless electron-phonon coupling constant. Significantly, our study sheds light on the gaps which have recently been observed in different iron-pnictide CSs as nodes or line-nodes on the Fermi surface and have evinced considerable interest.
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G. Malik, I. Chávez and M. Llano, "Generalized BCS Equations and the Iron-Pnictide Superconductors," Journal of Modern Physics, Vol. 4 No. 4, 2013, pp. 474-480. doi: 10.4236/jmp.2013.44067.
 Y. Kamihara, T. Watanbe, M. Hirano and H. Hosono, “Iron-Based Layered Superconductor La[O1-xFex]FeAs (x = 0.05 - 0.12) with Tc = 26 K,” Journal of the American Chemical Society, Vol. 130, No. 11, 2008, pp. 3296-3297.
 H. Takahashi, K. Igawa, K. Arii, Y. Kamihara, M. Hirano and H. Hosono, “Superconductivity at 43 K in an Iron-Based Layered Compound La1-xFexFeAs,” Nature, Vol. 453, No. 7193, 2008, pp. 376-378. doi:10.10/nature06972
 K. Ishida, Y. Nakai and H. J. Hosono, “To What Extent Iron-Pnictide New Superconductors Have Been Clarified: A Progress Report,” Journal of the Physical Society of Japan, Vol. 78, 2009, Article ID: 062001.
 P. M. Aswathy, J. B. Anooja, P. M. Sarun and U. Syamaprasad, “An Overview on Iron Based Superconductors,” Superconductor Science and Technology, Vol. 23, No. 7, 2010, Article ID: 073001.
 G. P. Malik, “On the Equivalence of Binding Energy of a Cooper Pair and the BCS Energy Gap: A Framework for Dealing with Composite Superconductors,” International Journal of Modern Physics B, Vol. 24, No. 9, 2010, p. 1159. doi:10.1142/S0217979210055408
 G. Mu, H. Luo, Z. Wang, L. Shan, C. Ren and W. Wen, “Low Temperature Specific Heat of the Hole-Doped Ba0.6K0.4Fe2As2 Single Crystals,” Physical Review B, Vol. 79, No. 17, 2009, Article ID: 174501.
 L. Shan, Y. Wang, B. Shen, B. Zeng, Y. Huang, A. Li, et al., “Observation of Ordered Vortices with Andreev Bound States in Ba0.6K0.4Fe2As2,” Nature Physics, Vol. 7, 2011, pp. 325-331. doi:10.1038/nphys1908
 H. Ding, P. Richard, K. Nakayama, K. Sugawara, T. Arakane, Y. Sekiba, et al., “Observation of Fermi-SurfaceDependent Nodeless Superconducting Gaps in
Ba0.6K0.4Fe2As2,” Europhysics Letters, Vol. 83, No. 4, 2008, Article ID: 47001. doi:10.1209/0295-5075/83/47001
 C. Ren, Z. Wang, H. Luo, H. Yang, L. Shan and W. Hai-Hu, “Evidence for Two Energy Gaps in Superconducting Ba0.6K0.4Fe2As2 Single Crystals and the Breakdown of the Uemura Plot,” Physical Review Letters, Vol. 101, No. 25, 2008, Article ID: 257006.
 P. Popovich, A. V. Boris, O. V. Dolgov, A. A. Golubov, D. L. Sun, C. T. Lin, et al., “Specific Heat Measurements of Ba0.6K0.4Fe2As2 Single Crystals: Evidence for a Multiband Strong-Coupling Superconducting State,” Physical Review Letters, Vol. 105, No. 2, 2010, Article ID: 027003.
 Y. Zhang, L. X. Yang, F. Chen, B. Zhou, X. F. Wang, X. H. Chen, X. H., et al., “Out-of-Plane Momentum and Symmetry-Dependent Energy Gap of the Pnictide
Ba0.6K0.4Fe2As2 Superconductor Revealed by Angle-Resolved Photoemission Spectroscopy,” Physical Review Letters, Vol. 105, No. 11, 2010, Article ID: 117003.
 F. Seitz, “The Modern Theory of Solids,” McGraw Hill, New York, 1940.
 G. P. Malik and U. Malik, “On the Calculation of Tc’s of Superconducting Binary Alloys Based on Two-Phonon Exchange Mechanism,” Physica B, Vol. 348, No. 1-4, 2004, pp. 341-346. doi:10.1016/j.physb.2003.12.009
 G. P. Malik, “Generalized BCS Equations: Applications,” Internantional Journal of Modern Physics B, Vol. 24, No. 19, 2010, p. 3701. doi:10.1142/S0217979210055858
 G. P. Malik and U. Malik, “A Study of the Thallium- and Bismuth-Based High-Temperature Superconductors in the Framework of the Generalized BCS Equations,” Journal of Superconductivity and Novel Magnetism, Vol. 24, No. 1-2, 2011, pp. 255-260. doi:10.1007/s10948-010-1009-0
 J. M. Blatt, “Theory of Superconductivity,” Academic Press, New York, 1964, p. 206.
 D. Lee, “Iron-Based Superconductors: Nodal Rings,” Nature Physics, Vol. 8, 2012, pp. 364-365.
 Y. Zhang, Z. R. Ye, Q. Q. Ge, F. Chen, J. Jiang, M. Xu, B. P. Xie, et al., “Nodal Superconducting-Gap Structure in Ferropnictide Superconductor BaFe2(As0.7P0.3)2,” Nature Physics, Vol. 8, 2012, pp. 371-375.
 M. P. Allan, A. W. Rost, A. P. Mackenzie, Y. Xie, J. C. Davis, K. Klhou, et al., “Anisotropic Energy Gaps of Iron-Based Superconductivity from Intraband Quasiparticle Interference in LiFeAs,” Science, Vol. 336, No. 6081, 2012, pp. 563-567. doi:10.1126/science.1218726