Superconductivity

The Meissner Effect in action! Here one can see the expulsion of a magnetic field as the superconductor transitions to a super-conducting state

(By, Kevin Le)

The worst part about physics is its laws.  Although they explain how just about everything works, they also remind us of how limited the universe’s capabilities are.  The laws of physics are the reason why people cannot fulfill their hopes of having superpowers, and why the planet is slowly dying – energy is not perpetual, and so we tear up resources as a result.  However, there is still hope in the form of superconductivity.  If the three laws of thermodynamics say that there is no such thing as a free meal, then superconductivity ends world hunger.  Send a current through a superconducting wire, and the current will never lose any energy to resistance.  Levitate a magnet above a superconductor, and the Sun will die out before the magnet falls.

Discovered in 1911 by Dutch physicist Heike Kamerlinger Onnes and his colleagues, scientists everywhere reveled at the thought of near-infinite energy.  However, there was a catch.  Superconductors require frigid temperatures to be maintained, and even “high-temperature” superconductors only work below 130 K (minus 143 Celsius, minus 225.7 Fahrenheit).  And if that was not enough, superconductors lose their resistance-defying abilities if they are exposed to too large a magnetic field or too strong an electrical current.  Due to the price of maintaining superconductors, superconductors have failed to become a major presence in society.

As a superconductor cools, it gradually loses resistance in the same way most other conductive materials lose resistance until the superconductor reaches its critical temperature, a point at which resistance suddenly stops.  This is not a result of resistance simply disappearing, but rather instead, of the material going through a phase transition – like the effects of latent heat when water freezes or evaporates.  The reasoning behind this lies in magnetism.

When the atoms in a normal conductor give up electrons, they become positively-charge ions, which in turn creates a net attraction between the atomic lattice of positive ions and the negatively charged electrons passing through it.  Now, if the vibrations and deformations of all this was not enough, suppose magnets were bouncing around there too.  For normal conductors, this would increase the resistance of electricity greatly, but in superconductors it does the exact opposite.  Picture a pair of magnetized electrons (also known as “Cooper pairs”) passing through the ion lattice, one electron right behind the other.  When the first electron passes through, it attracts the surrounding atoms towards, and everything clumps together.  By concentrating multiple positive charges, a local area of greater positive charge is created, which is subsequently directly in front of the second electron.  Since electrons have negative charges and opposites attract in magnetism, the force pulling the second electron forward is increased.  In other words, the first electron is spending energy to get through the positively-charged lattice, but the second electron is being pulled through without having to use any energy due to magnetism.  Consequently, the average energy used breaks even and there is no resistance.

One common property of superconductivity is the Meissner Effect, which occurs when a magnet is placed above a superconductor.  The magnet will then appear to levitate by some invisible force.  In the Meissner Effect, the magnet has the effect of creating a “mirror-image” of itself within the superconductor.  As a result, the magnet and the superconductor will repel each other because the magnetic fields of the magnet cannot penetrate the superconductor.  The invisible lines of force between the two are expelled by the superconductor, and these lines push the magnet upward, thus making it appear to float in mid-air.

All in all, the potential of superconductors are monumental.  Already, superconductors have helped saved lives in MRI Machines and have made transportation much more efficient with the production of the extremely fast, albeit extremely expensive, Maglev trains.  Yet, because of the strict limitations superconductors have, and because of how expensive it is to maintain those conditions, it will still be a while before we reach an age of near-infinite energy.  Outside of unlimited energy, superconductors could be used to make force fields through the Meissner Effect, which in turn could be used to generate infrastructure instantaneously.  Hover boards, hover cars, and belts which could allow people to defy gravity would all become a reality as well.  And if the limitations of superconductors could be overcome, then all of this would be incredibly cheap.  As a result, a room-temperature superconductor has become the Holy Grail of solid-state physicists.  Embarrassingly enough, although there is an explanation for low-temperature superconductors, there is no theory for high-temperature superconductors, making the entire procedure hit-or-miss.  Today, a Nobel Prize awaits the scientist who can crack the code of high-temperature superconductors.  One day, that scientist may be the person reading this article right now.  After all, the worst part about physics may be its laws – but the best part is finding the exception.

Posted in How Things Work