Superconductivity Dance Flash Mob Video: Superconductivity Explained

Science meets Art: watch a science dance flash mob video and learn how electrons work together to create superconductivity (electricity without resistance) at The Emergent Universe, an online interactive science museum about emergence.

When Electrons FlashMob

How electrons behave in the superconducting state

In a metal, electrons flow like a gas thorough a grid of metal ions. When the temperature is above the critical temperature, Tc, and the superconducting material is in its normal, non-superconducting state, these electrons move nearly independently of one another. When the temperature drops below Tc and the material enters its superconducting state, these electrons, like the dancers here, pair up. The electron pairs can then lower the overall energy by synchronizing their movements with the other pairs, such that all pairs move cooperatively together as a single, coherent entity.

What’s an electron?

An electron is a tiny, negatively charged fundamental particle that obeys the laws of quantum mechanics. This means that sometimes an electron acts like a particle and sometimes it acts like a wave.

One or more electrons surround the nucleus in an atom. Electrons are also the carriers of electric current in a wire.

What’s a metal ion?

Ions are atoms that have too many or too few electrons. Because atoms are neutral and electrons are negatively charged, ions with too few electrons will be positively charged. In a metal, the atoms that form the solid grid have given up some of their electrons, becoming positively charged ions. The "lost" electrons flow through this ion grid and are available to carry electric current.

Why does superconductivity happen?

The grid of ions in a metal do not sit still; they vibrate like a plucked guitar string. In some metals, gas-like electrons, which would normally repel one another, can attract each other through their interaction with the vibrating ions. Thus, when one electron interacts with the vibrations the ion grid responds in such a way that a second electron is drawn towards the first, in the same way a bowling ball on a bed creates an indentation that would draw in a second bowling ball. This vibration-induced attraction between electrons drives the pairing that creates superconductivity.*

*This mechanism applies only to conventional superconductors. Electrons in the "high temperature" superconductors discovered in 1987 become attract each other through a somewhat different mechanism.

Why does superconductivity only occur below Tc?

The synchronization of the paired electrons in the superconducting state not only lowers the energy, but it also reduces the disorder (compared to the normal, non-superconducting state). Because disorder is preferred at higher temperatures (this is the reason why ice melts), the more disordered normal-state becomes preferred over the lower-energy, but less disordered superconducting-state when the temperature exceeds Tc.

Why is there no resistance in superconductors?

Recall that electric current is the net flow of electrons along a wire. In a normal, non-superconducting wire, electric current is reduced by resistance, that is, by the scattering of these electrons. In a superconductor, the electrons lower their energy by moving in a synchronized way. Consequently, it requires energy to break up this synchronization. Since scattering would break up this synchronization but is unable to provide enough energy to do so, scattering cannot occur. As a result, the superconducting current flows with no resistance.

Resources

General

Hyperphysics on the Bardeen, Cooper, Schrieffer electron-level explanation of superconductivity: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/bcs.html#c1

An explanation of BCS theory that emphasizes its quantum nature: http://www.superconductivity.eu/en/index.php#supra-explication

YouTube link for the superconductivity flash mob video: http://youtu.be/O6sukIs0ozk

DISCUSSION FORUM TITLE

The EmergentMatters Forum