Super Conductivity Josephsen Junctions

Super ConductivityJosephsen Junctions And SQUIDS

By: Keegan Warner

Outline

Superconductors

History

New technologiesApplication Josephson junctionsJosephson EffectJosephson Voltage StandardSQUIDSHow Squids workDC SquidsAC SquidsSuperconductors are Supercool

Superconductivity

Phenomenon of zero resistance in a superconductor when cooled below a certain temperature depending on the material

Only some materials can become a superconductors; materials like copper and silver retain some resistance even at absolute zero because of impurities or defects

Different than physics idea of perfect conductivity because it includes complete removal magnetic field lines from the superconductor Supercurrent: current flowing infinitely across a superconductor without any applied voltage

History

Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes

Using recently created liquid helium he was able to lower mercury to 4 K, at this point the resistance completely disappeared

1913 Lead was discovered to be a superconductor at 7 K1933 Meissner discovered superconductors expel their internal magnetic fields; named the Meissner effect1941 Niobium nitride was discovered to be a superconductor at 16 K1987 Peroskite (Ca Ti oxide) superconducts at 35 KThis marked an important step because it allows liquid nitrogen to be the coolant instead of liquid helium, which is much easier to use and produce

Recent superconductors

Scientists are continuously developing and experimenting for new higher temperature superconductors

1993 superconducting ceramics were discovered, up to 133 K

Highest ever recorded superconductorProblems with using ceramics extremely fragile and hard to shape2008 iron family of superconductors discoveredIron Oxygen Flouride superconducts up to 55 KNew predictions of superconductors working at higher temperature if you keep them under high pressuresHydrogen sulfide works at 80 K at 160 Gigapascals

Applications for superconductivity

Superconductors make the strongest electromagnets yet to known to man

These magnets are used in MRI machines and potentially in digital circuits in the future

Potential applications for power transfer with zero loss to resistanceSmart grid, power lines, maglev trains, magnetic levitation Also Josephson Junctions

Josephson Junctions

A device made from two superconductors separated by a weak thin insulator

Created when you separate two superconductors by a thin insulator a continuous current appears through the insulator

Predicted and published by Brian David Josephson in 1962 at his senior year at Cambridge when he was just 22It was heavily disputed by highly recognized scientists at the timeThe next year experiments in Bell labs proved his hypothesis Brian Josephson was awarded the Nobel prize for physics in 1973

Josephson Effect

On either side of the insulator the electrons in the superconductors get together into pairs, and those pairs get together to form a quantum wave

If the insulator is thin enough the quantum waves will spill through the insulator by a quantum tunneling effect, thus creating a current through the insulator

When you apply a fixed current across the junction the current across the insulator begins to alternate in frequency directly related to the voltageThis relationship within the superconductors isn’t affected by material properties This is important because a direct relation between frequency and voltage is not easily obtained

Josephson Voltage Standard

Josephson junctions create a direct relationship between frequency and voltage

Since frequency can be easily measured using standard atomic clocks throughout the world

Now scientists all over the world can use the Josephson junctions to create a voltage standard to calibrate their machines, this is called the Josephson voltage standardHowever the official SI unit has not been changed

SQUID’s

Super sensitive measuring device used to measure magnetic fields; a magnetometer

Uses two Josephson junctions in parallel in a superconducting loop

Can measure fields as low as 5 aT, 10 ^-18So far Squids are the most sensitive magnetometers ever created Can be used to measure magnetic fields in the brain in real timeUsed whenever scientists need a strong magnetometers Physics, archaeology, geology, biology

Creation of DC SQUIDS

First creation of SQUID was 1964 by Ford Research labs

Without any magnetic field the current is split equally across the two branches

When a magnetic field is applied a circular current forms around the loop creating a magnetic field to cancel out the introduced fieldWhen this induced current exceed the material's critical current, a voltage across the SQUID is inducedThis voltage can be measured and used to measure the magnetic field

Creation of AC SQUIDS

The first SQUID based on the AC Josephson effect was made in 1965 by Robert Jeklevic

Only uses one Josephson junction because the magnetic field will fluctuate with the AC voltage

AC SQUIDS have to be connected to resonant tanks where the changing magnetic field can be measuredAC SQUIDS are less sensitive but are easier to manufacture and maintain than DC SQUIDS

Superconductors are Supercool

Most Squids are made from traditional superconductors that have to be cooled by liquid helium

This limits Squids to only be used in a lab where the scientists can control the safety precautions of using liquid helium

Helium can freeze the air in the pipelines that causes dangerous pressure buildupsRecently Squids have been made using the high temperature superconductors possibly allowing Squids to be used in the field with liquid nitrogen

Conclusion

Superconductors are materials that when cooled to a certain temperature lose all their resistance and expel magnetic field

Josephson Junctions are two superconductors separated by a small insulator where there is a current that tunnels through the insulator

Josephson junctions directly relate voltage and frequency, this can be used to create a universal standard for the VoltSquids are created from Josephson junctions and are super powerful magnetometersSuperconductors are Supercool

References

Ame Ee Science Studio (4/10/2017) Josephson Effect

http://www.supraconductivite.fr/en/index.php?p=applications-squid-josephson

Christopher L Henley (2011) Josephson Junctionshttp://www.lassp.cornell.edu/clh/BT-GL/6.5AD.pdfFagaly (2006) Superconducting Quatum Interference Device Instruments and Applications. Review of Scientific InstrumentsR Nave (4/10/2017) Superconductivity http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/scond.htmlJosephson Effect. 27 march 2017. In Wikipedia. Retrieved 4/10/2017Superconductivity. 5 April 2017. In Wikipedia. Retrieved 4/10/2017Brain David Josephson. 1 April 2017. In Wikipedia. Retrieved 4/10/2017

Key concepts

Superconductors lose all resistance when cooled past certain temperature and expel magnetic fields within the material

Josephson junctions create a direct relationship between voltage and frequency

With the direct voltage frequency relationship there is a worldwide reproducible voltage standard called the Josephson voltage standard Squids are super powerful magnetometers using josephson junctions to detect magnetic fieldsTraditional superconductors must be kept cold with liquid helium but new superconductors are being discovered that can use liquid nitrogen instead