Europhys. Lett.
Volume 69, Number 1, January 2005
Page(s) 121 - 127
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 08 December 2004
Europhys. Lett., 69 (1), pp. 121-127 (2005)
DOI: 10.1209/epl/i2004-10303-6

$\sin(2 \varphi)$ current-phase relation in SFS junctions with decoherence in the ferromagnet

R. Mélin

Centre de Recherches sur les Très Basses Températures (CRTBT) Boîte Postale 166, F-38042 Grenoble Cedex 9, France

received 14 June 2004; accepted in final form 26 October 2004
published online 8 December 2004

We propose a theoretical description of the $\sin(2 \varphi)$ current-phase relation in SFS junctions at the 0- $\pi$ crossover obtained in recent experiments by Sellier et al. (Phys. Rev. Lett., 92 (2004) 257005, cond-mat/0406236), where it was suggested that a strong decoherence in the magnetic alloy can explain the magnitude of the residual supercurrent at the 0- $\pi$ crossover. To describe the interplay between decoherence and elastic scattering in the ferromagnet, we use an analogy with crossed Andreev reflection in the presence of disorder. The supercurrent as a function of the length R of the ferromagnet decays exponentially over a length $\xi$, larger than the elastic scattering length ld in the absence of decoherence, and smaller than the coherence length $l_{\varphi}$ in the absence of elastic scattering on impurities. The best fit leads to $\xi \simeq \xi_h^{({\ab{diff}})}/3$, where $\xi_h^{({\ab{diff}})}$ is the exchange length of the diffusive system without decoherence (also equal to $\xi$ in the absence of decoherence). The fit of experiments works well for the amplitude of both the $\sin\varphi$ and $\sin(2 \varphi)$ harmonics.

74.50.+r - Tunneling phenomena; point contacts, weak links, Josephson effects.
74.78.Fk - Multilayers, superlattices, heterostructures.

© EDP Sciences 2005