Feb. 18, 2012Brian Utter

SuperconductivitySaturday Morning Physics

Heike Kamerlingh-OnnesDutch physicist

University of Leiden(1853 – 1926)

The Race to the Bottom

Sir James DewarScottish chemist

Royal 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)

(Non-super) ConductivityEach electrons moves fast (around 1,000,000 m/s)…

Not quite right, but like “microscopic Plinko”http://www.youtube.com/watch?v=D9MywMWgTq4&feature=fvst

In 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.

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=2673

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?

At low temperature, the resistance gets small, but is limited by impurities.

Another Experiment

current sent through resistor

voltage across resistor (proportional to

resistance)

thermocouple(larger voltage = lower

temperature)

“Kwik nagenoeg nul” translated as “Mercury practically zero”meaning mercury’s resistance was practically zero at 3K.

The Original Notebook

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.

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

Another Experiment

Superconductors 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.

Meissner EffectExpulsion of magnetic fields

http://www.youtube.com/watch?v=hksy_4Zmh80

normal conductor superconductor

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”).

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.

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.

Ok, so I got my superconductor. Cool.Now what?

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!)

Josephson and SQUIDS

Leo 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"

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)

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.

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)

High Tc Superconductors

YBaCuO

The “holy grail” is a room temperature superconductor.

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"

Theoretical Understanding

Alexei A. Abrikosov, Vitaly L. Ginzburg, and Anthony J. Leggett (2003), "for pioneering contributions to the theory of superconductors and superfluids."

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)

MagLev Trains

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_Qm0RJCXhc

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?