Crossed Andreev Reflection in Nanowire Based Hybrid Devices – Niels Bohr Institute - University of Copenhagen

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Crossed Andreev Reflection in Nanowire Based Hybrid Devices

We report on a study of the non-local Andreev process (cross Andreev reflection = CAR) in mesoscopic N-S devices defined in (i) planar metal-based structures that consist of a superconducting (S) Al wire with several normal metal (N) fingers and (ii) in semiconducting InAs nanowires in the quantum-dot regime.

For device (i) we measure the non-local differential resistance at a N detector located outside the current path, while a bias current is driven from another N injector contact to the S wire. In a small window of contact resistances, crossed Andreev reflection (CAR) can dominate the nonlocal transport for all energies below the superconducting gap. Besides CAR, elastic cotunneling (EC) and nonlocal charge imbalance can be identified as competing subgap transport mechanisms in temperature dependent four-terminal nonlocal measurements.

In type (ii) devices that are based on InAs nanowires (NWs) we have studied the splitting of Cooper pairs from a central S contact into two different quantum dots defined within the same NW. When the quantum dots are biased off-resonant, we measure a positively correlated current which is in agreement with Cooper pair splitting. In contrast, when we position the sensing quantum dot on resonance, the Cooper pair tunneling through one quantum dot is enhanced over Cooper pair splitting. Gaining control of crossed Andreev reflection (or Cooper pair splitting) is an important step towards the realization of a solid state entangler.

Nanophysics seminar by Prof. Christian Schönenberger, University of Basel