Issue
EPL
Volume 88, Number 1, October 2009
Article Number 17012
Number of page(s) 5
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI http://dx.doi.org/10.1209/0295-5075/88/17012
Published online 26 October 2009
EPL, 88 (2009) 17012
DOI: 10.1209/0295-5075/88/17012

Pairing of Cooper pairs in a Josephson junction network containing an impurity

Domenico Giuliano1 and Pasquale Sodano2

1   Dipartimento di Fisica, Università della Calabria and INFN, Gruppo Collegato di Cosenza, Arcavacata di Rende, I-87036, Cosenza, Italy, EU
2   Dipartimento di Fisica, Università di Perugia and INFN, Sezione di Perugia, Via A. Pascoli, I-06123, Perugia, Italy, EU

giuliano@fis.unical.it
sodano@pg.infn.it

received 6 August 2009; accepted in final form 16 September 2009; published October 2009
published online 26 October 2009

Abstract
We show how to induce pairing of Cooper pairs (and, thus, 4e superconductivity) as a result of local embedding of a quantum impurity in a Josephson network fabricable with conventional junctions. We find that a boundary double sine-Gordon model provides an accurate description of the dc Josephson current patterns, as well as of the stable phases accessible to the network. We point out that tunneling of pairs of Cooper pairs is robust against quantum fluctuations, as a consequence of the time reversal invariance, arising when the central region of the network is pierced by a dimensionless magnetic flux $\varphi=\pi $. We find that, for $\varphi=\pi $, a stable attractive finite coupling fixed point emerges and point out its relevance for engineering a two-level quantum system with enhanced coherence.

PACS
74.20.Mn - Nonconventional mechanisms (spin fluctuations, polarons and bipolarons, resonating valence bond model, anyon mechanism, marginal Fermi liquid, Luttinger liquid, etc.).
74.81.Fa - Josephson junction arrays and wire networks.
75.10.Pq - Spin chain models.

© EPLA 2009