Dresden 2009 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 28: Superconductivity: Heterostructures, Andreev Scattering, Proximity Effect, Coexistence
TT 28.4: Vortrag
Mittwoch, 25. März 2009, 16:15–16:30, HSZ 105
Crossed Andreev reflection and dynamical Coulomb blockade — •Andreas Baumgartner, Andreas Kleine, Jelena Trbovic, and Christian Schönenberger — Institute of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
A natural source of entangled electrons is the nonlocal process of crossed Andreev reflection (CAR) [1]. In CAR the two electrons of a Cooper pair in a superconductor coherently tunnel into two spatially separated normal metal contacts. This process is expected to produce a negative nonlocal voltage, Unl, in a four terminal device with two normal (injector and detector) and two superconducting contacts. However, recent experiments have shown that elastic cotunneling (EC) and charge imbalance (CI) lead to Unl>0 and can mask CAR [2].
In this contribution we show that Unl can be negative for all subgap biases, which suggests that CAR can dominate all other processes, as required for a solid-state entangler. We fabricated a series of lateral multiterminal Al/Al2O3/Pd hybrid structures with contact distances smaller than the superconducting coherence length and with different barrier resistances. We show that for a small window of injector and detector resistances CAR is the dominant nonlocal subgap process, and that for larger resistances the CAR and CI rates are reduced. We tentatively ascribe these systematic changes with barrier resistance to dynamical Coulomb blockade [1].
[1] Recher et al., PRL 91, 267003 (2003).
[2] Cadden-Zimansky et al., PRL 97, 237003 (2006), Russo et al., PRL 95, 027002 (2005), Beckmann et al., PRL 93, 197003 (2004)