Superconductors Josephson junctions

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. 

One of the features first observed in BaPbj B Og, and now known as a hallmark of bulk ceramic superconductors is the appearance of grain boundary Josephson junctions. One of the most... 

In 1962, B. Josephson recognized the implications of the complex order parameter for the dynamics of the superconductor, and in particular when one considers a system consisting of two bulk conductors connected by a weak link." This research led to tile development of a series of weak link devices commonly called Josephson junctions. See also Josephson Tunnel-Junction. These devices hold much promise for achieving ultra high-speed computers where switching time is of the order of 1CT11 second. 

Fig. 15. Two superconductors separated by a thin layer of insulator (a) and the two parallel Josephson junctions (b). 1, 2, Metals 3, 4, the layers of dielectric.

We found out that interlayer tunneling I-V characteristics at low temperatures essentially differ from those of conventional Josephson junctions between s-wave superconductors. We specify [14] 1) Jc(0) is strongly reduced to compare with the value expected from Ambegaokar-Baratoff (A-B) relation, J(U1 (0) = KO nAa / 2es 2) quadratic and scaling behaviour of [Pg.185]

In 1962 a postgraduate student, Brian Josephson, working in the University of Cambridge, and later to win a Nobel Prize, predicted that Cooper pairs should be able to tunnel through a thin (approximately 1 nm) insulating barrier from one superconductor to another with no electrical resistance [46]. This quantum tunnelling was confirmed by experiment and is known as the Josephson effect . The superconducting electronic devices exploit Josephson junctions. 

Josephson110 Effect. If two superconductors are separated by a thin layer (<3 nm for an insulator, several micrometers for a metal), then both a DC Josephson effect and an AC Josephson effect can occur. In the DC Josephson effect, a supercurrent can bridge the layer by quantum-mechanical tunneling, but there is a change in phase, which can be detected. It is very sensitive to magnetic fields indeed the supercurrent has the form f = f0 sin (O/O0)/ 7i(/0), where I0 depends on the temperature and the structure of the junction. If a DC potential V is applied across a Josephson junction, then the AC Josephson effect creates a response at a frequency... 

The Josephson junction is one such ultrafast superconducting switching device. Josephson junctions, which until recently operated only at liquid-helium temperature, are traditionally made of niobium-tin or niobium-germanium and are really simple connections between superconductors. They can do everything vacuum tubes and transistors do, but a lot faster. 

Josephson junction A type of electronic circuit capable of switching at very high speeds when operated at temperatures approaching absolute zero. Composed of two superconductors that are separated by a thin nonsuperconducting layer in which electrons can cross through the insulating barrier, it was discovered by... 

Keywords Quantum bit, Josephson junction, d-wave superconductors. 

A Josephson junction consists of two closely spaced superconductors separated by a weak connection (Figure 4.6.1). This connection may be provided by an insulator, a normal metal, a semiconductor, a weakened superconductor, or some other material that weakly couples the two superconductors. The two superconducting regions may be characterized by quantum mechanical wave functions and 2 respectively. Normally a much more complicated description would be necessary because... 

We now give a more quantitative discussion of the Josephson effect. Suppose that a Josephson junction is connected to a de current source (Figure 4.6.2), so that a constant current I >0 is driven through the junction. Using quantum mechanics, one can show that if this current is less than a certain critical current, no voltage will be developed across the junction that is, the junction acts as if it had zero resistance However, the phases of the two superconductors will be driven apart to a constant phase difference 0 = 0 - 0, where 0 satis-... 

The intrinsic sampler resolution is essentially determined by the ratio of current density to specific capacitance of a Josephson junction pulser contained in the sampling circuit. For picosecond resolution with existing helium temperature superconducting technologies, junction current densities are approaching 104 to 105 A/cm2. The upper end of this is at the limit that has presently been demonstrated for the YBaCuO superconductor itself at 77 K, so achieving such density in a junction will be a major challenge. 

A similar behavior is observed in the oxide barrier Josephson junctions. We can think of these junctions as formed by two superconductors separated by a thin insulator (Figure 10). Let us call... 

The next step in the development of high thin-film devices after the optimization of single layer films is the introduction of defects in precisely defined positions in order locally to alter the properties of the superconductor. The use of grain boundaries as Josephson junctions in SQUlDs (Superconducting Quantum Interference Devices) is an example of how defects can be utilized. 

Godfrey, Stephen. Carleton University Department of Physics. Superconductors BCS Theory, Josephson Junctions, SQUIDS, etc. Available from . 

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