Josephson effects, superconducting

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. 

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],... 

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. 

Josephson junction A superfast, superconducting electronic switch based on the Josephson effect. 

Because the first models of the physics of superconductivity were based on the phenomenon of Bose-Einstein condensation (BEC) it is not surprising that the existence of the Josephson effect has also been postulated for cold-atom systems in the BEC state [11]. In both superconductors and BEC cold-atom systems, the Josephson effect arises from the approximation of non-conservation of particle number, which gives rise to a phase type of order parameter F(x) and concomitant wave phenomena, described at T = 0 by the Gross-Pitaevski equation " ... 

The Josephson effect is the phenomenon in which two superconducting materials weakly coupled through a non-superconducting interface show a sharp increase in conductance of current flowing from one of the superconductors to the other if radiation of a suitable frequency is applied to the interface. The relation between the voltage difference between the two superconductors Uj and the frequency / of the applied radiation for which there is an increase in current is given by... 

Low-magnetic-field applications. These applications include Josephson-effect devices, magnetic-flux shields, transmission fines, and resonant cavities, all of which require superconducting materials having a high critical temperature and a high critical magnetic field. 

Josephson Effect. Another major development in understanding how superconductivity works came in 1962 when Welsh physicist Brian Josephson, a twenty-two-year-old graduate student, predicted the tunneling of electrons and Cooper pairs between linked superconductors. Within a year, experiments proved that pairs could travel across a barrier as easily as single electrons. In 1973Josephson shared the Nobel Prize in Physics with physicists Leo Esaki and Ivar Gi-aever, who had also worked on tunneling. 

Potential applications of superconductors are based on the properties that these materials present (i) zero resistance below Tc, (ii) Josephson effect, (iii) Meissner effect, and (iv) superconducting magnets. 

MG Wicks, PR Haycocks, T Hori. AC Josephson effect in superconducting niobium nitride tunnel junctions at up to 2.5 THz. Electron Lett 26 610, 1990. 

Josephson B D 1962 Possible new effects in superconductive tunnelling Phys. Lett. 1 251... 

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... 

We have considered here the influence of dispersion asymmetry and Zee-man splitting on the Josephson current through a superconductor/quantum wire/superconductor junction. We showed that the violation of chiral symmetry in a quantum wire results in qualitatively new effects in a weak superconductivity. In particularly, the interplay of Zeeman and Rashba interactions induces a Josephson current through the hybrid ID structure even in the absence of any phase difference between the superconductors. At low temperatures (T critical Josephson current. For a transparent junction with small or moderate dispersion asymmetry (characterized by the dimensionless parameter Aa = (vif — v2f)/(vif + V2f)) it appears, as a function of the Zeeman splitting Az, abruptly at Az hvp/L. In a low transparency (D Josephson current at special (resonance) conditions is of the order of yfD. In zero magnetic field the anomalous supercurrent disappears (as it should) since the spin-orbit interaction itself respects T-symmetry. However, the influence of the spin-orbit interaction on the critical Josephson current through a quasi-ID structure is still anomalous. Contrary to what holds... 

The current status of investigations of spin valve effects in structures composed of superconducting and ferromagnet layers is briefly reviewed. The main difficulties on the way of realization of SF spin valve devices are outlined. It is demonstrated that some of them can be effectively overcome by the use of trilayer femomagnetic - normal metal -ferromagnet structures as a weak link of Josephson junctions. 

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