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 Δ σ , 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. d I ( V ) / d V -spectra of SnS-Andreev contacts based on MgB2 samples (with defects of crystal structure), and Mg1−xAlxB2 polycrystalline samples (with the local critical temperature T C variation 10 K ≤ T C ≤ 37 K ) were studied by means of the “break-junction” technique within the temperature range 4.2 K ≤ T ≤ T C .