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Temperature Dependence of Superconducting Gaps in Mg(Al)B2 System Investigated by SnS-Andreev Spectroscopy

Detailed temperature dependence of both superconducting gaps was obtained directly by means of SnS-Andreev spectroscopy. The Δσ,π(T) -curves were shown to be deviated from standard BCS-like behavior, due to k-space proximity effect between σ- and π- condensates, which could give a key to experimental determination of interband electron-phonon coupling constants. For the first time, an excellent qualitative agreement with theoretical predictions of Nicol and Carbotte, and Moskalenko and Suhl was shown. dI(V)/dV-spectra of SnS-Andreev contacts based on MgB2 samples (with defects of crystal structure), and Mg(Al)B2 polycrystalline samples (with the local critical temperatures Tc variation 10 K < Tc < 37 K) were studied by means of the "break-junction" technique within the temperature range 4.2 K < T < Tc.