Full counting statistics of crossed Andreev reflection

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Abstract

We calculate the full transport counting statistics in a three-terminal tunnel device with one superconducting source and two normal-metal or ferromagnet drains. We obtain the transport probability distribution from direct Andreev reflection, crossed Andreev reflection, and electron transfer which reveals how these processes' statistics are determined by the device conductances. The cross-correlation noise is a result of competing contributions from crossed Andreev reflection and electron transfer, as well as antibunching due to the Pauli exclusion principle. For spin-active tunnel barriers that spin polarize the electron flow, crossed Andreev reflection and electron transfer statistics exhibit different dependencies on the magnetization configuration, and can be controlled by relative magnetization directions and voltage bias.

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Proximity effects in superconductor-ferromagnet heterostructures

A. I. Buzdin (2005)

The very special characteristic of the proximity effect in superconductor-ferromagnet systems is the damped oscillatory behavior of the Cooper pair wave function in a ferromagnet. In some sense, this is analogous to the inhomogeneous superconductivity, predicted long time ago by Larkin and Ovchinnikov (1964), and Fulde and Ferrell (1964), and constantly searched since that. After the qualitative analysis of the peculiarities of the proximity effect in the presence of the exchange field, the author provides a unified description of the properties of the superconductor-ferromagnet heterostructures. Special attention is paid to the striking non-monotonous dependance of the critical temperature of the multilayers and bilayers on the ferromagnetic layer thickness and conditions of the realization of the "Pi"- Josephson junctions. The recent progress in the preparation of the high quality hybrid systems permitted to observe on experiments many interesting effects, which are also discussed in the article. Finally, the author analyzes the phenomenon of the domain-wall superconductivity and the influence of superconductivity on the magnetic structure in superconductor-ferromagnet bilayers.

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Odd Triplet Superconductivity and Related Phenomena in Superconductor-Ferromagnet Structures

K Efetov, F S Bergeret, A. F. Volkov (2005)

We consider novel unusual effects in superconductor-ferromagnet (S/F) structures. In particular we analyze the triplet component (TC) of the condensate generated in those systems.This component is odd in frequency and even in the momentum, which makes it insensitive to non-magnetic impurities. If the exchange field is not homogeneous in the system the triplet component is not destroyed even by a strong exchange field and can penetrate the ferromagnet over long distances. Some other effects considered here and caused by the proximity effect are: enhancement of the Josephson current due to the presence of the ferromagnet, induction of a magnetic moment in superconductors resulting in a screening of the magnetic moment, formation of periodic magnetic structures due to the influence of the superconductor, etc. We compare the theoretical predictions with existing experiments.

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A spin triplet supercurrent through the half-metallic ferromagnet CrO2

G. Miao, G. Xiao, A. Gupta … (2006)

In general, conventional superconductivity should not occur in a ferromagnet, though it has been seen in iron under pressure. Moreover, theory predicts that the current is always carried by pairs of electrons in a spin singlet state, so conventional superconductivity decays very rapidly when in contact with a ferromagnet, which normally prohibits the existence of singlet pairs. It has been predicted that this rapid spatial decay would not occur when spin triplet superconductivity could be induced in the ferromagnet. Here we report a Josephson supercurrent through the strong ferromagnet CrO2, from which we infer that it is a spin triplet supercurrent. Our experimental setup is different from those envisaged in the earlier predictions, but we conclude that the underlying physical explanation for our result is a conversion from spin singlet to spin triplets at the interface. The supercurrent can be switched with the direction of the magnetization, analogous to spin valve transistors, and therefore could enable magnetization-controlled Josephson junctions.