Josephson-effect

Ideally a standard cell is constmcted simply and is characterized by a high constancy of emf, a low temperature coefficient of emf, and an emf close to one volt. The Weston cell, which uses a standard cadmium sulfate electrolyte and electrodes of cadmium amalgam and a paste of mercury and mercurous sulfate, essentially meets these conditions. The voltage of the cell is 1.0183 V at 20°C. The a-c Josephson effect, which relates the frequency of a superconducting oscillator to the potential difference between two superconducting components, is used by NIST to maintain the unit of emf. The definition of the volt, however, remains as the Q/A derivation described. 

B. D. Josephson (Cambridge) theoretical predictions of the properties of a supercurrent through a tunnel barrier, in particular those phenomena which are generally known as the Josephson effects. 

Superconducting electronic devices are in a different class. They rely on two phenomena the Josephson effect and the quantisation of magnetic flux, which are described in a simple way in ref. [46], while a more complete account is given in ref. [47],... 

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. 

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The quantized nature of vortices has been studied in these materials by various techniques including microwave Josephson effect... 

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The Josephson effects are of a quantum mechanical nature. For the qualitative description of the Josephson effects one can use the simple... 

To analyze the Josephson effects let us consider the current through the insulating layer which separates two superconductors [Fig. 15(a)]. Let T, and T2 be the wave function of the electron pair on either side of the junction. For simplicity, both superconductors are assumed to be similar. Following Feynman et al. [40], we use the following time-dependent Schrodinger equations for T, and T2... 

Equations (27) describe the first two Josephson effects. With the lack of voltage, the junction is traversed by the current which can be equal to any value between + J0 and — J0 depending on what the value of the d0 phase is. When a constant external voltage is applied, the current oscillates with the... 

Summary. We consider the Josephson effect in a ballistic Superconductor/ Quantum Wire/ Superconductor junction. It is shown that the interplay of chiral symmetry breaking generated by Rashba spin-orbit interaction and Zeeman splitting results in the appearance of a Josephson current even in the absence of any phase difference between the superconductors. 

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. 

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. 

A comparison between theory and experiment for the fine structure intervals in helium holds the promise of providing a measurement of the fine structure constant a that would provide a significant test of other methods such as the ac Josephson effect the and quantum Hall effect. The latter two differ by 15 parts in 108 and are not in good agreement with each other [59]. 

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. 

To compare the theory of ae with experiment, it is necessary to know the value of a, which has been measured in diverse branches of physics. Currently best values of a, with relative standard uncertainty of 1 x 10-7 or less, are those based on the quantum Hall effect [32], the ac Josephson effect [25], the neutron de Broglie wavelength [33], the muonium hyperfine structure [34,35], and an absolute optical frequency measurement of the Cesium >1 line [36] ... 

Thus for a determination of a from a g factor measurement it would be desirable to choose an ion where Z is sufficiently high to get a small uncertainty in a but the influence of higher order QED contributions is not too large. Ca19+ seems to be a good choice. If we assume the same experimental accuracy on that ion as presently obtained in C5+ we would obtain a fractional uncertainty in a of 8 10-8. This is comparable to other present determinations of a from Quantum Hall or Josephson effect. The envisaged improvement in the experimental g factor by one order of magnitude would make the a determination competitive with that extracted from the g factor of the free electron. 

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 RF SQUID is based on the AC Josephson effect, uses only one Josephson junction, and is less sensitive than the DC SQUID, but is cheaper and easier to manufacture its SQUID is inductively coupled to a resonant tank circuit. Depending on the external magnetic field, as the SQUID operates in the resistive mode, the effective inductance of the tank circuit changes, thus changing the resonant frequency of the tank circuit. These frequency measurements can be easily done, and thus the losses that appear as the voltage across the load resistor in the circuit are a periodic function of the applied magnetic flux with a period of 0. 

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,... 

Josephson effect When electron pairs pass through a thin, insulating barrier between two superconductors without resistance. 

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