JOSPHSON JUNCTION

Guided by- submitted by-Prof. Ajit Satapathy Sai Smruti NayakEEE deaprtment (1101298116)

Josphenson junction

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Outline of Presentation Introduction

Superconductivity

Messiner – Oschenfield effect

Josephson Equations

Types of Josephson Effect

Cooper pair

Application

References

JOSEPHSON JUNCTION• A Josephson junction is a type of electronic circuit capable of switching at very high speeds

when operated at temperatures approaching absolute zero.

• The ability of certain materials to conduct electric current with practically zero resistance.

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Superconductivity In 1911 superconductivity was first observed in mercury by Dutch physicist Heike Kamerlingh Onnes.

Definition :

Property of some materials to exhibit zero electrical resistance and the exclusion of interior magnetic field, known as Meissner’s effect, below critical temperature is known as Superconductivity.

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Types Of Superconductors

Type I Superconductors :

Have critical temperature range of less than 1K to 20 K. e.g. Niobium, Tantalum, Magnesium Diboride, some highly doped semi-conductors.

Type II Superconductors :

Have high critical temperature. e.g. cuprate perovskite family compounds(YBa2Cu3O7).

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Messiner – Oschenfield effect There is complete expulsion of magnetic field from the interior of the Superconductor. The magnetic inductance becomes zero when it is cooled below TC in a week magnetic field HC, above which superconductivity disappears. This field is temperature dependent. The expulsion of magnetic flux causes source magnetic energy.

So long as this cost is less than the consideration energy gained by going from the normal to the superconductivity becomes too large, the cost in magnetic energy will outweigh the gain in consideration energy, and the super conduction will become partially or totally normal.

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Messiner – Oschenfield effect

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Types of Josephson Effect1. DC Josephson Effect In absence of biasing voltage.

I= Ic sin Φ.

2. AC Josephson Effect When a bias voltage is applied.

δΦ/δt= 2eV/h.

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DC Josephson EffectAccording to Brian Josephson, if two superconductors are separated by a sufficiently thin layer of insulator (10 A thick), weak superconducting currents can tunnel through the potential barrier without any applied voltage, that is, the resistance is zero. In a given superconductor, the pairs are represented byΨ= ΨO ejΦ where Φ is the phase and is the same for every pair. They are said to be “phase coherent”.The super current through the barrier is related to the phase difference on the left and right sides of the junction. If the superconductor on the left has phase Φ1 and that on the right has phase Φ2, Josephson showed.

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AC Josephson EffectJosephson predicted that when a finite voltage V is applied across the junction there will be a flow of current. Solution to Schrödinger’s equation gives the expression for current asI = Ic sin [∂ (0) + [(2eV/h) t] (6.4)This shows that current oscillates with frequency ωj=2eV/h where V is the applied voltage, h is the constant; e is the basic electronic charge. If V is a constant then the phase difference can be given by the equation ∂=∂ (0) + ωj t. Then d∂/dt = ωj. That is the ratio of change of phase difference is directly proportional to the applied voltage.

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Cooper pair Electron pairs coupling over range of hundreds of nanometers are called cooper pair.

These coupled electron can take character of boson and condense into ground state.

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FabricationThere are three layers :

Superconductor

Insulating layer-

Non-oxide layer e.g. Magnesium fluoride or diamond-like carbon

OR oxide layer e.g. BaSnO3.

Another superconductor .

Followed by a final sealing and coating.

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Fabrication(contd..)

Reference- Aharon Z. Hed, “Method of Making a Josephson Junction”, U.S. Patent, 5171732, Dec 15,1992.

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Applications Magnetic Sensors

Gradiometers

Oscilloscopes

Decoders

Analogue to Digital converters

Samplers

Oscillators

Microwave amplifiers

Sensors for biomedical, scientific and defense purposes

Digital circuit development for Integrated circuits

Microprocessors

Random Access Memories (RAM’s)

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CONCLUSIONWith the advent of such junctions working on the principle of superconductivity brought about a link between different branches of study to give us efficient and highly advanced technology.

Before Josephson's prediction, it was only known that normal (i.e. non-superconducting) electrons can flow through an insulating barrier, by means of quantum tunneling. Josephson was the first to predict the tunneling of superconducting Cooper pairs. For this work, Josephson received the Nobel prize in physics in 1973.[5] Josephson junctions have important applications in quantum-mechanical circuits, such as SQUIDs, superconducting qubits, and RSFQ digital electronics. The NIST standard for one Volt is achieved by an array of 19,000 Josephson junctions in series

References1. K. K. Likharev, “Dynamics of Josephson Junction and circuits”

(Gordon and Breach, New York, 1986).

2. M.S.Vijaya, G.Rangarajan, “Materials Science”, (Tata McGraw-Hill,2004).

3. J.Clarke, “The New Superconducting Electronics”,

(Kluwer Dordrech,1993).

4. Insang Song, Yunsung Huh and Gwangseo Park, “Microwave Coupling Of The Josephson Junction Arrays With An External Source”, IEEE Transactions On Applied Superconductivity, vol-7, June, 1997

5. M. Tachiki, S. E. Shafranjuk, “Vortex Lattice Structure And Josephson Junction Plasma in High Tc Superconductors”,Chinese Jounal Of Physics, vol-36, April, 1998.

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