Department of Physics, NCU
Title
Electron transport in hybrid superconducting devices
Speaker
Vladimir Bubanja
Measurement Standards Laboratory of New Zealand, Callaghan Innovation, Wellington, New Zealand
The Dodd-Walls Centre for Photonic and Quantum Technologies, University of Otago, Dunedin, New Zealand
Date 2016.08.02 (Tue.)
Time 10:30-12:00
Place S4-625
Abstract
Nanoscale tunnelling structures in a low temperature environment provide the basis for development of metrological sources of electric current. The new definition of the ampere, scheduled to be adopted in 2018, will be based on the exact numerical value of the elementary charge, e, and in practice will be realised by utilising sources that transfer electrons one by one. For this purpose we analyse the operation of hybrid turnstiles, consisting of a combination of superconducting and normal metal electrodes, and consider ways to improve the accuracy by suppressing the undesirable multi-electron tunnelling processes. In the case of a turnstile consisting of normal metal electrodes, separated by insulating layers from the superconducting island (NISIN), the main mechanisms that limit the accuracy of the device are elastic and inelastic cotunneling processes. On the other hand, in the case of a SINIS turnstile, the dominant errors are caused by the Andreev reflection and Cooper-pair-electron cotunneling. We show that by choosing the appropriate on-chip circuit impedance these devices can be designed to satisfy the stringent metrological requirements on accuracy. It is often the case in precision metrology that the pursuit of high accuracy leads to understanding of new physics. In the case of single electron sources, the errors in the device operations that need to be suppressed, lead to advances in understanding of non-equilibrium phenomena of quantum multi-electron processes. While these processes are detrimental to the operation of the single-electron devices in metrological applications, interestingly they perform the key function in information processing applications. We consider the electron spin transport, in hybrid superconducting structures, in the processes involving the simultaneous tunnelling of several electrons. We show that under appropriate conditions nontrivial spin transport occurs between distant unconnected electrodes.