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 Delta(sigma,pi)(T)-curves were shown to be deviated from standard BCS-like behavior, due to k-space proximity effect between alpha- and pi-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. dl(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 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. (C) 2011 Elsevier Ltd. All rights reserved.