Myung-Chul Jung, Chang-Jong Kang, B. I. Min, K. -W. Lee
Two recently uncovered isostructural superconductors LaNiBN (T_c=4.1 K) and LaPtBN (T_c=6.7 K) were investigated using the ab-initio electron and phonon band structure calculations. The electronic structures are found to be substantially three-dimensional, leading to them being metallic in both NiB (PtB) and the intervening LaN layers. Our full phonon calculations show that the electron-phonon coupling (EPC) is contributed from almost all phonon modes, except for unusually isolated and high energy optical modes due to B and N ions, implying that the superconductivity is attributed from the both layers. For LaNiBN, our calculations show an EPC strength of \lambda=0.52 and a logarithmically averaged characteristic phonon frequency of \omega_{log}= 376 K, leading to T_c= 3.9 K for the Coulomb pseudopotential \mu*= 0.12. Compared with the Ni B_{1g} mode in LaNiBN, the Pt B_{1g} mode in LaPtBN is reduced by ~70%, leading to a slightly enhanced \lambda=0.56 and a \omega_{log} reduced to ~20%. Using \mu*= 0.1, our calculated T_c is 5.4 K for LaPtBN, which is consistent with the experiment. Additionally, we cannot find any indication of magnetic instability through various calculations. Therefore, our results unambiguously indicate that both systems are conventional EPC mediated superconductors.
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http://arxiv.org/abs/1303.3324
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