Crossed Andreev Reflection in Nanowire Based Hybrid Devices

Nanophysics seminar by Prof. Christian Schönenberger, University of Basel

Abstract:


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.