Josephson effect, observation

The quantum of magnetic flux is only 2.07 x 10-15 Wb, which is approximately equal to the amount of the earth s magnetic field enclosed by a ring of 10p,m in diameter. The Josephson effect is observed when two superconductors are separated by a very thin insulating layer (about 20 nm). Single electrons and Cooper pairs can tunnel through such a layer. The characteristics of the Josephson junction are now used to define the volt and have enabled the uncertainty in the maintained standard to be reduced to 0.1 p,V. 

We will see that the unusual character of the superconductivity in the transversal direction leads to peculiarities of the Josephson effect. For example, if the bias current flows through the terminal superconducting layer So and Sa (see Fig. 3), the supercurrent is zero because of the different symmetry of the condensate in So and Sa- In order to observe the Josephson effect in this structure the bias current has to pass through the layers Sa and Sb, as shown in Fig. 3. The supercurrent between S and S b is non-zero because each superconductor has its own TC and the phase difference tp is finite. 

Examples of the observational equations are given in Table 2. In that table, r H and vb are transition frequencies in hydrogen and deuterium such as those given in Table 3 below, Kj is the Josephson constant, which is characteristic of the Josephson effect, and Rk is the von Klitzing constant, which is characteristic of the quantum Hall effect. Note that Ex(riLj)/h is proportional to cRoo and independent of h, hence h is not an adjusted constant in these equations. 

That pairs are at work in the new ceramics has been demonstrated by measurements of what is known as the Josephson effect, named after the physicist Brian D. Jo-sephson, who observed it in 1961 as a graduate student at Cambridge University in England. The Josephson effect,... 

As a 22-year-old graduate student, Brian Josephson (1962) suggested that it should be possible for a current to pass between the two superconductors, even if there were no voltage difference between them. Although this behavior would be impossible classically, it could occur because of quantum mechanical tunneling of Cooper pairs across the junction. An observation of this Josephson effect was made by Anderson and Rowell in 1963. 

Josephson affects Electrical effects observed when two superconducting materials (at low temperature) are separated by a thin layer of insulating material (typically a layer of oxide less than 10 m thick). If normal metallic conductors are separated by such a battier it is possible for a small current to flow between the conductors by the turmel effect. If the materials are superconductors (see suPERCONDUcnvTTY), several unusual phenomena occur ... 

In 1962, Josephson predicted that if two superconducting metals were placed next to each other separated only by a thin insulating layer (such as their surface oxide coating) then a current would flow in the absence of any applied voltage. This effect is indeed observed... 

The property of the spin-triplet components fi,2,z un) = — /i,2,3(—w ) means that their presence is not easy to observe. For example, the order parameter A is related to the sum X n=-oo /(wn) in which all contributions of the odd functions f 1,2,3 cancel. However, there are phenomena where the presence of the spin-triplet pairing plays a crucial role. One of them is the effect of the Tc dependence on the mutual orientation of magnetizations in the F/S/F structure. Another one is the predicted long-range proximity effect based on the spin-triplet component, which should lead to a Josephson current in F/S/F/S structures with anomalously thick F-layers.[10] The latter is relevant for experimental results of Ref. [5]. 

Anderson, P. W., and Rowell, J. M. (1963) Probable observation of the Josephson superconducting tunneling effect. Phys. Rev. Lett. 10, 230. 

It is now generally agreed, however, that the observed increase in results from suppression of charge density wave formation rather than some exotic quasi-two-dimensional mechanism. However, the effect of the two-dimensional anisotropy of the material is of considerable interest. It has been found that the critical field behavior is in broad agreement with theoretical predictions based on a model of a layered compound containing two-dimensional superconducting layers weakly coupled via Josephson tunneling. ... 

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