Nanoscale physics

Charge transport through superconducting nanodevices
Belogolovskii M.1,2, Zhitlukhina E.2,3, Seidel P.2
1 Kyiv Academic University, National Academy of Sciences of Ukraine, Vernadsky blvd 36., 03142 Kyiv, Ukraine
E-mail: belogolovskii@ukr.net
2 Institut für Festkörperphysik, Friedrich-Schiller-Universität, Helmholtzweg 3, 07743 Jena, Germany
3 O. O. Galkin Donetsk Institute for Physics and Engineering, National Academy of Sciences of Ukraine, Nauki Ave 46, 03028 Kyiv, Ukraine

Any practically used device includes a combination of different materials and/or potential barriers. This makes it important to study and understand new characteristics that are emerging in their interface region. When the devices are nanoscale, quantum effects become increasingly important and enter in a natural way through the superconductivity (S), non-locality and quantum coherence. This work discusses a scattering matrix formalism to quantum electron transport in complex nanoscale multilayers formed by materials with different charge orderings. We argue that such approach is typically more transparent and efficient for coherent conductors than conventional kinetic equation or Green's function methods. It is demonstrated on the examples of planar NI1NS1I2S2 heterostructures, where N is a non-superconducting (magnetic or non-magnetic) nm-thick conducting film and I is an insulating barrier, as well as Josephson junctions with an (NF)nN multilayered barrier.
The idea behind the scattering approach to quantum charge transfer in meso- and nanodevices is to decompose the problem into elementary scattering events and calculate their total contribution by summing coupled convergent series. We have used numerical results obtained for NI1NS1I2S2 nanoscale junctions for explaining unusual conductance dips in the above-gap region of quasiparticle excitations spectra observed previously by various groups. It is shown that superparamagnetic ordering in the (NF)nN weak link generates random magnetic fluctuations that strongly affect charge transfer through related Josephson junctions. We argue that such nanodevices can be used to implement low-temperature p-bites for stochastic computing and some other applications usually associated with pure quantum circuits.
E.Zh. acknowledges financial support from Deutscher Akademischer Austauschdienst (DAAD) under the grant “Non-unitary quantum devices as p-bites for stochastic computing”, the funding programme 57552335. M.B. is grateful for the financial support from Volkswagen Stiftung under the grant 9B884 “Novel quantum platforms for cryogenic sensing and stochastic computing”.