PhysicsAugust 20, 2019

Superconductivity

Materials that conduct (transport) electricity with no resistance and expel magnetic fields

What is superconductivity?

Superconductors are materials that conduct (transport) electricity with no resistance. This means a superconductor can carry an electrical current indefinitely without losing any energy.

So, once set in motion, an electrical current will flow forever in a closed loop of superconducting material.

Another important property of superconductors is that no magnetic field can exist in a superconductor. Instead, the magnetic field lines bend around the superconductor. This is called the Meissner effect.

But there’s one problem: superconductors only exist at low temperatures. The highest temperature achieved (and verified) for a superconductor is -70℃.

Here’s the reason why.

Materials are generally split into two categories based on their ability to conduct electricity. Metals (copper and silver) allow electrons to move and carry an electric charge. Insulators (wood and rubber) hold onto their electrons and do not allow an electric current to flow.

Superconductors are regarded as a third category of materials. Unlike metals, superconducting electrons pair together, which allows them to travel easily.

However, when we approach room temperature, the electron pairs break into single electrons and the material behaves like a metal.

The temperature at which a material changes to a superconductor is called the transition temperature.

There are two types of superconductors: Type I and Type II. Type I superconductors transition from their normal state to superconducting state instantly. Type II transition slowly, usually over a few degrees in temperature.

Type II superconductors tend to have a higher transition temperature compared to Type I.

There is a theory (the BCS Theory) to explain Type I superconductors, but we don’t yet understand what causes Type II superconductors.

So what?

Superconductors are used in Magnetic Resonance Imaging (MRI) machines to generate a large magnetic field. This gives doctors a non-invasive way to image the human body.

If you place a superconductor near a strong magnet, this causes electrical currents to flow on the surface of the superconductor. These electrical currents generate their own magnetic field, which counteracts the original magnetic field. This causes the superconductor to levitate above the magnet. This is the principle behind today’s Maglev trains.

Superconducting magnets are also used in particle accelerators to bend and focus beams of colliding particles.

What else?

The race is on to find a room temperature superconductor. This would unleash a range of amazing technologies. For example, lossless energy transmission and storage. And hoverboards (yes, just like the ones in Back to the Future II).

Scientists are also trying to understand how this phenomenon occurs. If we could understand how superconductivity occurs then we could also predict likely candidates for room temperature superconductors.