1. Super Conductivity Josephsen Junctions And SQUIDS
By: Keegan Warner

2. Outline Superconductors Josephson junctions SQUIDS History
New technologies
Application
Josephson junctions
Josephson Effect
Josephson Voltage Standard
SQUIDS
How Squids work
DC Squids
AC Squids
Superconductors are Supercool

3. 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
* field exists on the edge of material for about 100nm
Something i thought was cool: Experiments have demonstrated that supercurrents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a current lifetime of at least 100,000 years. But Theoretically it could last forever

4. 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 K
1933 Meissner discovered superconductors expel their internal magnetic fields; named the Meissner effect
1941 Niobium nitride was discovered to be a superconductor at 16 K
1987 Peroskite (Ca Ti oxide) superconducts at 35 K
This 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
Niobium plus nitrogen. Only used as a superconductor and anti-reflective lenses
Peroskite Calcium Titanium oxide

5. 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 superconductor
Problems with using ceramics extremely fragile and hard to shape
2008 iron family of superconductors discovered
Iron Oxygen Flouride superconducts up to 55 K
New predictions of superconductors working at higher temperature if you keep them under high pressures
Hydrogen sulfide works at 80 K at 160 Gigapascals

6. 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 resistance
Smart grid, power lines, maglev trains, magnetic levitation
Also Josephson Junctions

7. 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 22
It was heavily disputed by highly recognized scientists at the time
The next year experiments in Bell labs proved his hypothesis
Brian Josephson was awarded the Nobel prize for physics in 1973

8. 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 voltage
This 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

9. 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 standard
However the official SI unit has not been changed

10. 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 ^-18
So far Squids are the most sensitive magnetometers ever created
Can be used to measure magnetic fields in the brain in real time
Used whenever scientists need a strong magnetometers
Physics, archaeology, geology, biology
Superconducting quantum interference device
aT = atto Tesla

11. 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 field
When this induced current exceed the material's critical current, a voltage across the SQUID is induced
This voltage can be measured and used to measure the magnetic field

12. 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 measured
AC SQUIDS are less sensitive but are easier to manufacture and maintain than DC SQUIDS

13. 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 buildups
Recently Squids have been made using the high temperature superconductors possibly allowing Squids to be used in the field with liquid nitrogen
Helium solid frozen air that blocks pipe lines and causes dangerous pressure buildup

14. 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 Volt
Squids are created from Josephson junctions and are super powerful magnetometers
Superconductors are Supercool

15. References Ame Ee Science Studio (4/10/2017) Josephson Effect
Christopher L Henley (2011) Josephson Junctions
Fagaly (2006) Superconducting Quatum Interference Device Instruments and Applications. Review of Scientific Instruments
R Nave (4/10/2017) Superconductivity
Josephson Effect. 27 march In Wikipedia. Retrieved 4/10/2017
Superconductivity. 5 April In Wikipedia. Retrieved 4/10/2017
Brain David Josephson. 1 April In Wikipedia. Retrieved 4/10/2017

16. 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 fields
Traditional superconductors must be kept cold with liquid helium but new superconductors are being discovered that can use liquid nitrogen instead
A list of five concepts, key points, or discussions from your presentation that could be used as a basis for questions on our Final Exam! Your colleagues in our class will use these lists and your posted presentations as Final Exam study material!!!