Nanoscale physics

Novel nanoscale superconducting switch
  Zhitlukhina E.1, Dvoranová M.2, Plecenik T.2, Gregor M.2, Roch T.2, Grančič B.2, Satrapinskyy L.2, Belogolovskii M.3, Kúš P.2, Plecenik A.2
1 Department of Phase Transitions, Donetsk Institute for Physics and Engineering of the NAS of Ukraine. Prospect Nauki, 46, Kyiv-03028, Ukraine.
E-mail: elena_zhitlukhina@ukr.net
2 Faculty of Mathematics, Physics and Informatics, Comenius University in Bratislava, Mlynská dolina F2, 842 48 Bratislava, Slovakia.
3 Joint Research Laboratory for Dynamics of Electronic Processes in Hybrid Structures, G.V. Kurdyumov Institute for Metal Physics, Academician Vernadsky Boulevard, 36, Kyiv-03142, Ukraine.

A novel device based on the resistive-switching phenomenon in nm-thick transition-metal oxide interlayer separating two layers, a superconductor (S) and a normal (N) counter-electrode, is proposed. It enables to modify the transparency of the N/S interface over a wide range and thus to probe the S spectra in two limiting regimes, a perfect (without any barrier) contact and a tunneling-like configuration.
We have verified the technique by creating point contacts between Pt and Nb with a nanoscale Al2O3/TiO2 interlayer in the low-resistance state. Niobium was chosen as the metal of interest since its Eliashberg function 2F() has been previously reconstructed in tunneling experiments. Our figure of merit was the differential conductance G(V) = dI(V)/dV. We modified the conventional BTK formalism by replacing the constant gap value Nb with a function (E) in order to take into account the phonon-induced structure and introducing a constant imaginary part into the electron energy E  E +i where  is the Dynes parameter. By fitting the conductance spectrum G(V) measured at 4.2 K up to the critical temperature we obtained Nb(4.2 K) = 1.4-1.5 meV in a good agreement with the literature data while the smearing Dynes parameter (4.2 K) ≤ 2(4.2 K) was unusually large. Moreover, predicted by our numerical calculations features at ~ 16 meV and ~ 23 meV related to transversely polarized and longitudinal Nb phonons have been well reproduced experimentally. Resuming, we argue that oxygen-vacancies filaments generated in the Al2O3/TiO2 low-resistance state realizes an ultra-narrow direct contact of a Pt electrode with the Nb surface.
E. Zhitlukhina is deeply grateful to the Slovak Academic Information Agency for the support of her stay at the Comenius University in Bratislava. M. Belogolovskii is thankful to the Targeted Research & Development Initiatives Programme funded by the STCU and the National Academy of Science of Ukraine (Project No. 6250).