Feb. 18, 2012 Brian Utter Saturday Morning Physics

Heike Kamerlingh-Onnes Dutch physicist University of Leiden (1853 – 1926) The Race to the Bottom Sir James Dewar Scottish chemist Royal Institute of London ( ) 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) Conductivity Each electrons moves fast (around 1,000,000 m/s)… Not quite right, but like “microscopic Plinko” 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 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?

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.

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!

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 Effect Expulsion of magnetic fields

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 SQUIDS In 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 T c 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 T c Superconductors YBaCuO  The “holy grail” is a room temperature superconductor.

High T c 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

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

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?