All About Superconductivity

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Podcast Transcript

In 1911, a Dutch physicist named Heike Kamerlingh Onnes was experimenting with ultra low-temperature metals. He was measuring the electrical resistance of mercury to find out what would happen 

What he found was shocking and totally upended everything we know about physics and electricity.

Learn more about superconductivity, how it works, and its applications, on this episode of Everything Everywhere Daily.

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To understand what superconductivity is, we first have to understand what conductivity is, and its reciprocal value, resistance. 

When an electrical current passes through something, usually a metal, the ease with which it passes through it is its conductivity. Each substance will have different conductivity. Silver and copper have very high conductivity which is why they are often used for electrical wiring or for electrical contacts. 

Likewise, substances with poor conductivity, and high resistance, have a use as well. Incandescent lightbulbs work because they provide electrical resistance. The resistance causes the filament to get hot and glow. Likewise, the burner on an electrical stove, or an electrical space heater both produce heat from electrical resistance.

So, high conductivity is great for things like wires where you want to transmit electricity and high resistivity is great for other applications like producing heat.

However, even a great conductor like copper doesn’t have perfect conductivity. When you have more of a substance, like a very long wire, you will have more resistance. This becomes a huge problem for things like long-distance electrical transmission. The longer the distance you transmit electricity, the more that will be lost during the transmission. 

Here I’m going to skip back to the physicist I mentioned in the introduction: Heike Kamerlingh Onnes.

Prior to his experiments, there was debate amongst physicists as to what would happen to metals at very low temperatures when a current was run through them.

William Thomson, aka Lord Kelvin, thought that all electrical current would stop at very low temperatures. Any conducting substance would become a perfect resistor at some point.

However, other physicists like Onnes thought that the exact opposite would happen. That any metallic conductor would instead become a perfect conductor. 

On April 8, 1911, at 4 pm, Onnes resolved the question once and for all. 

He was running an experiment on a wire made of solid mercury which was in a bath of liquid helium. 

He was measuring the current on the wire as the temperature kept dropping.  When the temperature hit 4.19 Kelvin, something amazing happened.

All electrical resistance in the wire suddenly disappeared. Once it hit that temperature, the resistance went to zero and the mercury wire became a perfect electrical conductor. 

Onnes had discovered superconductivity. 

He continued to investigate this strange phenomenon. A year later he created a circular loop that was cooled down to near absolute zero. He put an electrical charge on it and removed the battery. What he found was that over time, the current in the loop didn’t decay. The current just kept going around and around in the loop.

He initially called it “supraconductivity” and later changed it to superconductivity.

Onnes was awarded the Nobel Prize in 1913 for his discoveries. 

Over time more and more substances were cooled down to extreme temperatures and tested for superconductivity. Most became superconducting at temperatures lower than mercury, but a few, like Lead and Niobium, were slightly higher, but still had very low temperatures.

In 1961 it was found that a substance of three parts niobium and one part tin could create incredibly powerful electromagnets, up to 10 or 20 times the strength of the most powerful natural magnets.

Superconductivity clearly had several amazing properties, but there was one massive problem. It only worked at extremely low temperatures around the boiling point of Helium, at 4 kelvin.

It was difficult to come up with practical applications for something which required temperatures so low. 

Despite all of the tests done on materials to check for superconductivity, it was believed going into the 1980s that nothing could be superconducting at a temperature higher than 30 kelvin, and the highest temperature superconductor known at that time was only around 25 kelvin.

In 1986, however, all this changed. 

A team at IBM managed to find a new type of copper oxide ceramic that achieved superconductivity at 35.1 Kelvin. 

Once the 30-kelvin threshold was passed and researchers knew it could be done, the race was on for the holy grail of superconductivity. A room-temperature superconductor. 

A room-temperature superconductor doesn’t, as the name implies, have to actually be room temperature, although if that could happen it would be incredible. 

What it mostly means is finding a superconducting material that is superconducting above 77 Kelvin or ?196.2° Celcius or  ?321.1° Farenheight, which is the boiling point of liquid nitrogen. 

Liquid nitrogen is relatively cheap and easy to make and store. 

If a true room-temperature superconductor were to be developed, it would revolutionize our world. It would allow for lossless transmission of electricity, reducing the amount of electricity that needs to be generated. It would allow us to connect the electrical grids of entire continents.

It could create amazing batteries that never lost their charge. Extremely powerful magnets could make magnetically levitating trains economically possible, and it could radically improve the efficiency of electrical power generation using turbines, create incredibly powerful quantum computers, make the containment of plasma in a fusion reactor more efficient, as well as a host of applications we haven’t even thought of yet.

Over the last 35 years, a race has been on to try and find a room-temperature superconductor and a lot of progress has been made. There is a category of materials called cuprates which have achieved superconductivity at 138 Kelvin or ?135° Celcius at normal atmospheric pressure.

If you are willing to increase pressure, by a whole lot, then there have actually been superconductors found at temperatures above the freezing point of water. In October 2020, researchers announced that they had created a carbonaceous sulfur hydride compound that was a superconductor at 15° Celcius or 59° Farenheight. 

However, it was only superconducting at 270 gigapascals which is the equivalent of the pressure inside the core of the Earth. 

Progress is slowly being made on the creation of a room-temperature superconductor. The upper temperatures of superconductivity keep increasing as new and innovative materials are tested. 

Nonetheless, even though they aren’t as efficient as they one day might be, superconductors are in use today. 

The biggest practical application of superconductors today is in Magnetic resonance imaging or MRI machines. They require incredibly powerful magnets and only superconducting magnets can really create that sort of magnetism. 

The Large Hadron Collider in Europe uses superconducting magnets as do many of the experimental fusion reactors now being tested. 

There are a handful of experimental projects around the world using superconducting cables for electrical transmission. So far, the longest is only 1 kilometer. 

Until the temperature of superconductivity can be raised substantially, it will be difficult to find uses cases for it. The cost of cooling simply makes it too difficult to use for all but the biggest budget projects. 

Hopefully, one day soon, we’ll have a room temperature breakthrough and the benefits to humanity might be as great as that of the internal combustion engine.