What Is a Superconductor? How Zero Electrical Resistance Was Discovered in 1911
My interest in superconductors began with a very simple question.
While watching a YouTube video, I came across the idea that if electrical resistance could be eliminated, it could reduce energy loss and the heat produced as electricity flows.
The first thing that came to mind was my smartphone.
Smartphone heat was one of the questions that first led me to learn about electrical resistance and superconductivity.
Anyone who has used a phone for a long time or played a demanding game has probably noticed how warm it can become. That made me wonder:
If a material really had zero electrical resistance, could it help reduce this kind of heat?
As I looked into the subject, I learned that smartphone heat is much more complicated than electrical resistance alone. Heat can come from many parts of a phone, including semiconductor power consumption, the battery, display, and wireless communication.
Still, that simple question was what led me to start learning about superconductors.
What Does Zero Electrical Resistance Actually Mean?
The wires, conductors, and electronic components we use every day normally have electrical resistance.
When electric current flows through resistance, some electrical energy can be dissipated as heat.
But certain materials behave very differently when cooled to sufficiently low temperatures. Below a particular temperature, their electrical resistance can disappear.
This condition is called the superconducting state, and materials capable of entering this state are called superconductors.
One important point is that a superconductor is not one particular material.
Many different materials can become superconducting under the right conditions. The temperature below which a material enters its superconducting state is generally called its critical temperature (Tc).
When I first heard the word "superconductor," I assumed it referred to some recently discovered advanced material.
Then I started looking into its history and found something I did not expect.
Superconductivity is not a recent discovery at all.
It was first observed in 1911.
It Started With Liquid Helium
One of the most important people in the early history of superconductivity was the Dutch physicist Heike Kamerlingh Onnes.
At Leiden University in the Netherlands, Onnes studied how materials behave at extremely low temperatures.
At the time, reaching such temperatures was a major scientific challenge.
In 1908, Onnes succeeded in liquefying helium.
Liquid helium made it possible to conduct experiments at temperatures much lower than had previously been practical.
A few years later, this achievement helped lead to an unexpected discovery.
1911: The Resistance of Mercury Disappears
In 1911, Onnes and his laboratory were studying the electrical resistance of mercury at extremely low temperatures.
As the mercury was cooled, its resistance changed.
Then, near 4.2 K, or about −269°C, something remarkable happened.
The electrical resistance of mercury suddenly dropped to a level that was effectively unmeasurable.
Onnes later described this dramatic change in his Nobel lecture, referring to a new state in which the resistance had essentially disappeared.
Today, this experiment is recognized as the first observation of superconductivity.
Why Was This Discovery So Important?
The resistance had not simply become a little smaller.
The material had entered a fundamentally different state.
In the superconducting state, electrical resistance disappears. This means that an electric current can flow without losing energy through ordinary electrical resistance.
At first glance, that sounds almost perfect for technologies such as electrical power systems and electronic devices.
But there was a major problem.
Mercury became superconducting only at around 4.2 K.
Absolute zero is 0 K, or approximately −273.15°C, so 4.2 K is only a few degrees above the lowest possible temperature.
In other words, discovering superconductivity and making superconductors practical for everyday use were two very different challenges.
Did Onnes Win the Nobel Prize for Discovering Superconductivity?
There is an interesting detail in this story.
Onnes received the Nobel Prize in Physics in 1913.
However, the official reason for the award was not simply "the discovery of superconductivity."
The Nobel Prize recognized his investigations into the properties of matter at low temperatures, which led, among other things, to the production of liquid helium.
The discovery of superconductivity emerged from this broader research into extremely low temperatures.
If It Was Discovered More Than 100 Years Ago, Why Is It Still a Future Technology?
After learning this history, I was left with an even bigger question.
Scientists had already observed electrical resistance disappearing in 1911.
So why, more than a century later, are superconductors still the subject of intense research?
And why do we continue to talk about superconductivity as a technology of the future?
I think understanding superconductivity means following this question through its history.
There is also another important part of superconductivity that goes beyond zero electrical resistance.
It involves the way superconductors interact with magnetic fields.
In 1933, scientists observed another phenomenon that became fundamental to our understanding of superconductivity.
It is known as the Meissner effect.
In the next article, I will explore the Meissner effect and why a superconductor cannot be fully understood simply as a material with zero electrical resistance.
References
NobelPrize.org — Heike Kamerlingh Onnes, Facts
NobelPrize.org — Heike Kamerlingh Onnes, Nobel Lecture
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