Temperature dependence of superconducting gaps in Mg1−xAlxB2 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)Δσ,π(T)-curves were shown to be deviated from standard BCS-like behavior, due to kk-space proximity effect between σσ- and ππ-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)/dVdI(V)/dV-spectra of SnS-Andreev contacts based on MgB2 samples (with defects of crystal structure), and Mg1−xAlxB2 polycrystalline samples (with the local critical temperature TCTC variation 10K≤TC≤37K) were studied by means of the “break-junction” technique within the temperature range 4.2K≤T≤TC.

► SnS-Andreev spectroscopy was used for Mg1−xAlxB2 (0≤x≤0.430≤x≤0.43) properties analysis.
► Detailed Mg1−xAlxB2 superconducting gaps temperature dependence was investigated.
► The σσ- and ππ-gap temperature dependences Δσ,π(T)Δσ,π(T) differ from each other.
► The data are in excellent qualitative agreement with theory of Moskalenko and Suhl.
► A kk-space proximity effect between two superconducting condensates was observed.