Brian Utter Super conductivity Saturday Morning Physics Heike Kamerlingh Onnes Dutch physicist University of Leiden 1853 1926 The Race to the Bottom Sir James Dewar Scottish chemist ID: 416158
Download Presentation The PPT/PDF document "Feb. 18, 2012" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Feb. 18, 2012Brian Utter
Super
conductivity
Saturday Morning PhysicsSlide2
Heike Kamerlingh-Onnes
Dutch physicistUniversity of Leiden(1853 – 1926)
The Race to the BottomSir James DewarScottish chemistRoyal Institute of London(1842-1923)By the mid-1800’s, the temperature of absolute zero was accurately predicted
1898 – Dewar liquefies hydrogen (20.28 K)
1898 – Dewar solidifies hydrogen (14.01 K)
1883 –
Wrobleski
liquefies nitrogen (77 K)
1908 –
Onnes
liquefies
helium
(4.2 K)Slide3Slide4
(Non-super) Conductivity
Each electrons moves fast (around 1,000,000 m/s)…
Not quite right, but like “microscopic Plinko”http://www.youtube.com/watch?v=D9MywMWgTq4&feature=fvstIn the end, electrons slowly “drift” along at about 1 meter per hour!! This is called electrical resistance.
… BUT, they are constantly bombarding the atoms in the material.
They
lose a lot of energy in collisions, which is lost as heat
.Slide5
An ExperimentOnnes
was interested in how the electrical properties of matter were affected by temperature. What happens with a “normal” conductor, like copper, if you measure the resistance as the temperature is decreased?
http://www.absorblearning.com/media/attachment.action?quick=11a&att=2673Slide6
An Experiment
Onnes
was interested in how the electrical properties of matter were affected by temperature. What happens with a “normal” conductor, like copper, if you measure the resistance as the temperature is decreased?At low temperature, the resistance gets small, but is limited by impurities.Slide7
Another Experiment
current sent through resistor
voltage across resistor (proportional to resistance)thermocouple(larger voltage = lower temperature)Slide8
“
Kwik
nagenoeg nul” translated as “Mercury practically zero”meaning mercury’s resistance was practically zero at 3K.The Original NotebookSlide9
The Nobel Prize in Physics 1913 was awarded to
Onnes
"for his investigations on the properties of matter at low temperatures which led to the production of liquid helium".Sudden drop to zero resistance below critical temperature.Slide10
Without
realizing it, they also observed the superfluid transition
-- two different quantum transitions seen for the first time in one lab on the same day!http://www.youtube.com/watch?v=2Z6UJbwxBZI Slide11Slide12
Another ExperimentSuperconductors exhibit “perfect conduction.”
But, there’s more weirdness – it’s not
just a perfect conductor. There are other behaviors that can’t be explained just as a conductor with zero resistance. It also exhibits the Meissner effect, discovered by German physicists Walther Meissner and Robert Ochsenfeld twenty years later in 1933.Slide13
Meissner Effect
Expulsion of magnetic fields
http://www.youtube.com/watch?v=hksy_4Zmh80Slide14
normal conductor
superconductorSlide15
An explanation, 5 dacades later:BCS Theory (1957)
John Robert Schrieffer , John Bardeen, and Leon Cooper who developed the BCS Theory of superconductivity, for which they were awarded the Nobel Prize in Physics in 1972 ("
for their jointly developed theory of superconductivity, usually called the BCS-theory”).Slide16
Ingredient #1: Cooper Pairs
Electron #1 deforms lattice of positive ions Electron #2 sees region of slightly higher positive charge Electron #2 is attracted to this slightly denser region and is therefore effectively attracted towards the first electron!!Cooper pairs are effective attractions between two electrons due to interaction with the solid lattice. Slide17
Ingredient #2: Bose-Einstein Condensate
Electrons travel together as waves, like light shining through the conductor, without bouncing off the atoms! The Cooper pairs are a superfluid – no dissipation!
Due to quantum mechanics, these electrons (which normally can’t occupy the same place) can pile up and exist in sync with each other.Slide18
Ok, so I got my superconductor. Cool.Now what?Slide19
Josephson and SQUIDSIn 1956, British physicist Brian Josephson predicted the behavior of current across a thin insulator between two superconductors (
quantum tunneling of Cooper pairs).
Used to make SQUIDs (Superconducting QUantum Interference Device) which can make sensitive measurements of magnetic fields. Fields as low as 10–18 T (100,000,000,000,000 times weaker than the Earth’s gravitational field!)Slide20
Josephson and SQUIDSLeo Esaki,
Ivar Giaever, and Brian D. Josephson (1973), "for their experimental discoveries regarding tunneling phenomena in semiconductors and superconductors, respectively,
" and "for his theoretical predictions of the properties of a supercurrent through a tunnel barrier, in particular those phenomena which are generally known as the Josephson effects"Slide21
Superconducting Magnets
In 1962, the first commercial superconducting wire, a niobium-titanium alloy, was developed by researchers at Westinghouse, allowing the construction of the first practical superconducting magnets.
(electromagnet == using a current to create a magnetic field)Slide22
Superconducting Magnets
Superconductors can maintain a current with
no applied voltage. Experiments show that currents in superconducting coils can persist for years without any degradation and a predicted lifetime of at least 100,000 years! Theoretical estimates for the lifetime of a persistent current can exceed the estimated lifetime of the universe!!e.g. used in MRI machines.Slide23
High Tc Superconductors
Before 1980, it was believed that 30 K was the highest possible temperature for a superconductor… until two researchers at Bell Labs discovered “YBCO” (a ceramic) with a critical temperature of 90K!
T(K)Slide24
High Tc
Superconductors
YBaCuO The “holy grail” is a room temperature superconductor. Slide25
High Tc Superconductors
The Nobel Prize in Physics 1987 was awarded jointly to J. Georg Bednorz and K. Alexander Müller
"for their important break-through in the discovery of superconductivity in ceramic materials"Slide26
Theoretical UnderstandingAlexei A.
Abrikosov, Vitaly L. Ginzburg
, and Anthony J. Leggett (2003), "for pioneering contributions to the theory of superconductors and superfluids."Slide27
Power Transmission
Holbrook Superconductor project, the world’s first transmission power cable transmitting waves of electricity from the grid to a substation that feeds
homes in Long Island. This project includes 99 miles of 138 kV high-temperature superconductor lines that are cooled with liquid nitrogen. (July 2008) Slide28
MagLev TrainsSlide29
MagLev Trains
The highest recorded speed of a maglev train is 581 km/h (361 mph), achieved in Japan by the CJR's MLX01 superconducting maglev in 2003
http://www.youtube.com/watch?v=V_Qm0RJCXhcSlide30
The first 100 years include strange behavior, unexpected explanations, and a variety of practical applications. A room temperature superconductor would open up a new world of uses. Is this impossible or the next revolution?