T. E. Kuzmicheva, S. A. Kuzmichev, M. G. Mikheev, Ya. G. Ponomarev, S. N. Tchesnokov, Yu. F. Eltsev, V. M. Pudalov, A. V. Sadakov, A. S. Usoltsev, E. P. Khlybov, L. F. Kulikova
We report the first observation of the intrinsic multiple Andreev reflections effect (IMARE) in S-n-S-...-S-arrays (S = superconductor, n = normal metal) formed by "break-junction" technique in GdO(F)FeAs superconductor (Tc = 48 - 53 K). We show that superconducting gap peculiarities at dI/dV-spectra sharpen dramatically in the arrays as compared with that in the single-contact spectra; this enables to improve significantly accuracy of the bulk superconducting parameters determination. Using IMARE, we determined the large and the small gap values \Delta_L = 11 +- 1.1 meV and \Delta_S = 2.6 +- 0.4 meV. The BCS-ratio 2\Delta_L/kTc^{local} = 5.0 - 5.9 > 3.52 (Tc^{local} is the contact area critical temperature) evidences for a strong electron-boson coupling. The results obtained agree well with our previous data by Andreev spectroscopy for single SnS-contacts.
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http://arxiv.org/abs/1302.5326
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