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Determination of the electron-phonon coupling constants from the experimental temperature dependences of superconducting gaps in MgB

JETP Letters, ISSN: 1090-6487, Vol: 99, Issue: 5, Page: 295-302
2014
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  • Citations
    17
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      17
  • Captures
    1

Article Description

Experimental temperature dependences Δ(T) of the energy of superconducting gaps for MgB samples with the critical temperatures 22 K < T < 41 K have been fitted by selecting the renormalized electron-phonon coupling constants λ with the use of the Moskalenko-Shul system of equations, the expression for the frequency of collective plasma oscillations obtained by Leggett for two-gap superconductors, and two fitting parameters. We previously obtained the dependences Δ(T) by the multiple Andreev reflection spectroscopy of superconductor-constriction-superconductor junctions based on MgB with various degree of disorder of the crystal structure. It has been shown that the intraband pairing constants are decisive for the superconductivity mechanism in MgB; in this case, √V V /V = 8-22 and the ratio of the interband constants α can range from 3 to 11. The set of the Eliashberg coupling constants λ has been qualitatively determined for relatively pure MgB with maximum values T ≈ 40 K. The leading constant is 0.7 < λ ≈ λ < 0.9 and depends on the choice of the upper integration limit in the Bardeen-Cooper-Schrieffer (BCS) model and the effective Coulomb repulsion μ . The characteristic ratio for the gap in the σ band is 2Δ/k T = 5.0-6.5. © 2014 Pleiades Publishing, Inc.

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