Letter abstract

Nature Physics 5, 393 - 397 (2009)
Published online: 26 April 2009 | doi:10.1038/nphys1252

Subject Categories: Condensed-matter physics | Electronics, photonics and device physics

Cooper-pair-mediated coherence between two normal metals

P. Cadden-Zimansky, J. Wei & V. Chandrasekhar


Two electrons bound in a singlet state have long provided a conceptual and pedagogical framework for understanding the non-local nature of entangled quantum objects. As bound singlet electrons separated by a coherence length of up to several hundred nanometres occur naturally in conventional Bardeen–Cooper–Schrieffer superconductors in the form of Cooper pairs, recent theoretical investigations1, 2, 3, 4, 5, 6, 7, 8, 9 have focused on whether electrons in spatially separated normal-metal probes placed within a coherence length of each other on a superconductor can be quantum mechanically coupled by the singlet pairs. This coupling is predicted to occur through the non-local processes of elastic cotunnelling and crossed Andreev reflection. In crossed Andreev reflection, the constituent electrons of a Cooper pair are sent into different normal probes while retaining their mutual coherence. In elastic cotunnelling, a sub-gap electron approaching the superconductor from one normal probe undergoes coherent, long-range tunnelling to the second probe that is mediated by the Cooper pairs in the condensate. Here, we present experimental evidence for coherent, non-local coupling between electrons in two normal metals linked by a superconductor. The coupling is observed in non-local resistance oscillations that are periodic in an externally applied magnetic flux.

  1. Physics and Astronomy Department, Northwestern University, Evanston, Illinois 60208, USA

Correspondence to: V. Chandrasekhar e-mail: v-chandrasekhar@northwestern.edu

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