Аннотация:The coherent transport in Josephson superconductor - normal metal - superconductor (S-N-S) and superconductor - ferromagnet - superconductor (S-F-S) nanocontacts attracts intense interest nowadays. Ferromagnetic materials suitable for Josephson S-F-S junction fabrication have the superconducting order parameter decay length of about several nanometers [1] which is much smaller compared to the decay length in normal metal. To increase the decay length in structures with ferromagnets di erent types of Josephson junctions with complex bilayered (NF) and trilayered (FNF) weak links have been proposed in
theoretical work [2]. We report the fabrication of planar Josephson S-N-S and S-NF-S junctions and their characterization down to T=300 mK. Samples were fabricated by electron beam lithography, using two-layer resist, and subsequent shadow deposition at two angles. We used aluminum lms with thickness of 100 nm like superconducting banks, while a 15-60 nm thick copper lm was used as a normal metal layer and 10 nm thick iron lm as a ferromagnetic one in a planar bilayered barrier. Two di fferent types of structures (S-N-S and S-NF-S) with the same geometry were investigated. It was found that current-voltage characteristics become hysteretic as temperature decreases despite the high transparency of SN-interfaces [2].. In the resistive part of current-voltage characteristics, the features related to the
multiple Andreev reections and the presence of a minigap were detected [3]. The nanofabricated S-NF-S structures of the second type had the space L between superconducting banks in the range of 30-200 nm. The Josephson supercurrent was observed in structures investigated. The critical current Ic of S-NF-S junctions was much smaller than that for S-N-S junctions. The rapid decrease of Ic with L increasing is due to the suppression of the superconducting proximity e ect by the F-layer. In the di erential resistance
(density of state) characteristics of S-NF-S junctions a double peak peculiarity was observed at the voltage corresponding to the minigap. The e ect observed can be explained by the induced electron spin polarization in the normal layer due to the ferromagnet.
References
[1] V. A. Oboznov, V.V. Bolginov, A. K. Feofanov, V. V. Ryazanov and A.I. Buzdin, Phys. Rev. Lett. 96, 197003 (2006). [2] T. Yu. Karminskaya, A. A. Golubov, M. Yu. Kupriyanov, and A. S. Sidorenko, Phys. Rev. B 81, 214518 (2010). [3] H. Courtois, M. Meschke, J. T. Peltonen, and J.P. Pekola, Phys. Rev. Lett. 101, 067002 (2008). [4] C. Cuevas, J. Hammer, J. Copu, J. K. Viljas, and M. Eschrig, Phys. Rev. B 73, 184505 (2006)
