Andreev-reflection-enhanced conductance of semiconductor-superconductor hybrid nanodevices

Date: 7 July 2016

Venue: University of Antwerp - Campus Groenenborger - Room U.241 - Groeneborgerlaan 171 - 2020 Antwerpen

Time: 4:00 PM - 5:00 PM

Organization / co-organization: Condensed Matter Theory

Short description: Department seminar presented by Dr Michal Nowak

Andreev reflection at a normal (N) – superconductor (S) interface corresponds to transfer of 2e charge through the junction. As a consequence, the conductance of a quantum point contact realized in the normal part of N-S junction is predicted to be quantized in twice the conductance quantum. However, the recent experimental realization of such a structure reveal an unexpected feature: despite a nearly perfect conductance quantization for electrons with energies above the superconducting gap, the conductance governed by Andreev reflection drops after the first enhanced plateau [1,2]. We investigate N-S junction defined in a proximitized nanowire and explain, that the lack of the conductance doubling is a result of mode mixing induced by residual disorder in the semiconductor. Furthermore, in a biased S-N-S junction, multiple conversions of Cooper pairs to electrons and vice-versa imprint the conductance with sub-gap features. Taking as an example Josephson junction defined in a 2DEG we demonstrate how the multiple Andreev reflections can be further exploited to infer transparency of the junction and to provide an estimate of the superconducting gap induced in the semiconductor [3].

[1] H. Zhang, Ö. Gül, S. Conesa-Boj, K. Zuo, V. Mourik, F. K. de Vries, J. van Veen, D. J. van Woerkom, M. P. Nowak, M. Wimmer, D. Car, S. Plissard, E. P. A. M. Bakkers, M. Quintero-Pérez, S. Goswami, K. Watanabe, T. Taniguchi, L. P. Kouwenhoven, arXiv:1603.04069 (2016).
[2] M. Kjaergaard, F. Nichele, H. J. Suominen, M. P. Nowak, M. Wimmer, A. R. Akhmerov, J. A. Folk, K. Flensberg, J. Shabani, C. J. Palmstrøm, C. M. Marcus, arXiv:1603.01852 (2016).
[3] M. Kjaergaard, H. J. Suominen, M. P. Nowak, A. R. Akhmerov, J. Shabani, C. J. Palmstrøm, F. Nichele, C. M. Marcus (to be submitted).

Dr. Michal  Nowak, TU Delft Theoretical Physics

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