Electricity and Magnetism

Superconductivity

Introduction

Imagine being able to ride a bike forever down a perfect road without needing to move the pedals. No wind resistance, no friction, no traffic getting in your way.  That is what electric conduction turns into in a superconducting material.  While electrons normally hit atoms at some points, under certain conditions and in some very special compounds, they can just run through the lattice with no losses.

 History

The phenomenom of perfect conduction was first reported by Dutch scientist Kamerlingh Onnes at the University of Leiden in the Netherlands in 1911.¹  He managed to liquify Helium and could then freeze Mercury to only a few degrees Kelvin.  At this temperature, current could be sent through a wire with no observed resistance.² Onnes called this characteristic suprageleider, which was later translated into superconductor.³

A milestone in supeconductivity research came in 1933 with the discovery of the Meissner Effect. Two German researchers, Meissner and Ochsenfeld found that a superconducting compound will completely exclude magnetic fields, thus creating an upward force on a magnet called magnetic levitation.⁴

Figure 1. A superconductor levitating an external magnet.⁵

 Why materials could behave this way when cooled was still unknown to science until the theory of Cooper pairs or the BCS theory were introduced by Bardeen, Cooper and Schrieffer in 1957.⁴ This is based on a rather complex quantum: coupling of two electrons with opposite momentum and spins.⁶ 

Due to the extreme costs accrued by cooling down to only a few degrees above absolute zero temperature, superconductivity remained a rather academic interest until the discovery of so called High Temperature Superconductors (HTS) in 1986 by two researchers at IT giant IBM.⁷  These special substances, most often compounds with Barium and/or Strontium, had a critical temperature up to 130 -  140 K. It should be noted that none of these materials occur naturally; they have to be manufactured using a special procedure.⁷

Recent years have seen another wave of discoveries of previously unknown superconductors, including a very recent revelation of of a special type of hydrogen sulfide capable of superconducting up to -70 degrees Centigrade.⁸

Research on superconducting materials and applications has yielded Nobel Prizes to Kamerlingh Onnes in 1913, Bardeen, Cooper and Schieffer in 1972, Bednorz and Müller in 1987, and physics prizes in 1962, 1973, 1978, 1996 and 2003 were also related to superconductivity in materials.⁹ 

Applications

The most obvious application of superconducting materials would be the perfect cable, running with no resistance in an eternal circuit. The costs of cooling has kept this to the prototype stage, seeing some installations in Denmark, the United States and Germany, but still not in use on a big scale.  This might come into effect more as superconducting materials can be manufactured more cheaply and cooling costs be reduced.

Magnetic levitation is used to create “flying” trains, where the car rides on a bed of superconductors and thus is suspended a distance above the line all the time. This has been tested extensively in Japan, and a line is being planned for construction with a target date for its completion of 2027.

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References

1. van Delft, D. and Kes, P.: The Discovery of Superconductivity. Physics Today, September 2010, pp. 38-43.
2. Slichter, C.: Introduction to the History of Superconductivity. American Institute of Physics, https://www.aip.org/history/mod/superconductivity/01.html .
3. Superconductivity entry at reference.com, http://dictionary.reference.com/browse/superconductor
4. Dull, Robert W. A Teacher’s Guide to Superconductivity for High School Students - Historical Background. Oak Ridge National Laboratory, http://web.ornl.gov/info/reports/m/ornlm3063r1/pt2.html
5. Magnetic Levitation – Wikipedia, the free Encyclopedia, https://en.wikipedia.org/wiki/Magnetic_levitation
6. Timm, C.: Theory of Superconductivity. Technical University of Dresden, http://www.physik.tu-dresden.de/~timm/personal/teaching/thsup_w11/Theory_of_Superconductivity.pdf
7. High-temperature Superconductivity - Wikipedia, the free Encyclopedia, https://en.wikipedia.org/wiki/High-temperature_superconductivity
8. Choi, Charles Q.: New Temperature Record is Huge Achievement for Superconducting, Live Science, http://www.livescience.com/51877-superconductors-new-temperature-record.html
9. Nobel Laureates in Superconductivity. IEEE Council on Superconductivity, http://ieeecsc.org/pages/nobel-laureates-superconductivity

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