The Future of Humanity Forged by Superconductivity

Yoji Ohashi (Professor, Department of Physics)

Even those who usually have little interest in physics have probably heard the term "superconductivity" somewhere. Superconductivity is a phenomenon, as shown in Figure 1, where the electrical resistance of a metal becomes completely zero below a certain temperature. It holds great promise not only for fundamental physics but also for engineering applications. In this article, I will introduce this phenomenon, which holds the potential to shape the future of humanity.

Why Does Superconductivity Occur?

The phenomenon of a metal's electrical resistance completely disappearing below a certain temperature was discovered in 1911 by the Dutch physicist Kamerlingh Onnes. At the time, there was a debate about what would ultimately happen to the electrical resistance of a metal as it was cooled. To settle this question, Onnes cooled mercury and discovered that its electrical resistance vanished at around 4 K (–269°C!). This "super" surprising phenomenon of zero electrical resistance = infinite electrical conductivity was named "superconductivity," reflecting that very surprise. The term "superconductivity" literally means "a state in which super-surprising electrical conduction occurs."

After Onnes's discovery, superconductivity was confirmed in various metallic substances other than mercury. However, it took a long time to elucidate the mechanism of this phenomenon, with the final answer being provided in 1957 by Bardeen, Cooper, and Schrieffer. Today, this theory is called BCS theory, after the initials of these three scientists. BCS theory subsequently had a major impact on the development of various fields, including not only superconductivity physics but also condensed matter physics, particle physics, nuclear physics, and astrophysics, and is hailed as a "monumental achievement of 20th-century physics." How does superconductivity work? To truly understand this, one needs knowledge not of "classical physics," which describes the physical phenomena we normally see, but of "quantum physics," which governs the microscopic world at the atomic level. However, on an "imaginary" level, it can be pictured as follows: In a normal metallic state (Figure 2, left), when electrons flow through a wire, they are obstructed by impurities and other obstacles, preventing them from moving straight, which gives rise to electrical resistance. In a superconducting state, however, as shown in Figure 2 (right), electrons form pairs, which then intertwine to form a large "mass" that flows in unison as an electric current. By moving as a collective "mass," they can overcome obstacles (impurities) that would have scattered individual electrons, allowing them to flow through the wire without resistance. To use an analogy, imagine a very bumpy road for a toy car. If you were to gather a large number of toy cars, melt them down (as wasteful as that sounds), and use the material to build a giant dump truck, it could drive over the road with ease. Of course, this is just an explanation at an imaginary level. After all, superconductivity is a phenomenon that is 100% quantum mechanical! Why do electrons form pairs (since electrons have a negative charge, they should normally repel each other and be unable to stick together!)? What does it mean for these pairs to intertwine and form a mass? Even if they flow in unison as a mass, wouldn't there still be some resistance? If your head is now filled with such questions, you are already captivated by superconductivity. If so, I encourage you to step into the world of physics.

Is Room-Temperature Superconductivity Possible?

Even if you were not convinced by the explanation of the mechanism of superconductivity above, you would likely agree that the "supernatural phenomenon" (though it is a real phenomenon) of electrical resistance becoming completely zero seems useful for many things. In particular, if power transmission lines were made of superconducting materials, it would be possible to transmit electricity with much thinner and lighter cables and with no power loss, which is expected to significantly improve energy and environmental problems.

So, are superconducting materials actually used in the power lines we see everywhere? The answer is no. In fact, each material has an upper limit to the temperature at which it can become superconducting (the superconducting transition temperature, Tc), and even the highest known Tc is below –100°C. In other words, no material that remains superconducting at everyday temperatures (room temperature, ~30°C)—a room-temperature superconductor—has been discovered yet, and superconducting power lines have not yet been realized.

What does it mean that more than 100 years after the initial discovery of superconductivity, a room-temperature superconductor has still not been found? According to Einstein's theory of relativity, it is impossible to travel faster than the speed of light (300,000 kilometers per second). Similarly, could it be that there is an upper limit imposed by the laws of nature on the superconducting transition temperature, and that this limit is below room temperature, meaning that room-temperature superconductors simply do not exist in nature?

The answer to this simple yet important question came in 2004 from research on a seemingly different system called a "superfluid Fermi atomic gas." This system consists of a gas of metal atoms like lithium or potassium. The group of atoms in the gas state enters a state identical to the superconducting state depicted in Figure 2 (right). Observations of this system revealed that the superconducting transition temperature, Tc, can only rise to about 20% of a characteristic parameter of the system called the Fermi degeneracy temperature (TF). Just as we feared, there is an upper limit to the superconducting transition temperature! So, is it higher or lower than room temperature? For a typical metal, the Fermi degeneracy temperature is around 10,000°C. Calculating from this, the upper limit for the superconducting temperature is about 2,000°C. This was a bit startling at first, but it means that room-temperature superconductivity (~30°C) is well within the realm of possibility (Figure 3). Since the laws of nature do not forbid it, the fact that room-temperature superconductivity has not yet been discovered must mean that humanity's efforts have been insufficient. Researchers involved in superconductivity research, including myself, must work tirelessly toward the discovery of a room-temperature superconductor.

Toward a Prosperous and Peaceful World Supported by a Global Energy Supply

The discovery of a room-temperature superconductor would undoubtedly be a Nobel Prize-worthy achievement. For those of you secretly thinking, "I'll win a Nobel Prize someday!", how about aiming for room-temperature superconductivity? However, the realization of room-temperature superconductivity has a much greater significance, one that makes the Nobel Prize money and medal seem trivial.

The foundations of human life are food and energy. With the global population continuing to grow rapidly, machinery is needed to increase food production to support it. In this sense, energy can be said to be the foundation of everything. Fossil fuels, which currently account for much of our energy supply, will eventually run out, and they also present the difficult problem of environmental issues. Nuclear energy, at present, is not in a situation where it has gained the understanding of everyone. However, for humanity to continue to develop sustainably, a stable energy supply that can also overcome environmental problems is absolutely necessary.

If room-temperature superconductivity were realized... what if we covered vast areas of land with little use, such as deserts around the world, with solar panels and supplied electricity to every corner of the globe via superconducting cables? We have already succeeded in distributing information to every corner of the world via the internet; room-temperature superconductivity would make it possible to do the same for energy. If we could stably supply electricity to regions suffering from poverty due to inadequate power supply using a network of superconducting cables, their living standards, starting with increased food production, would improve dramatically. Many of the conflicts that still exist around the world are related to poverty, and a dramatic improvement in the lives of people in conflict zones through a stable energy supply could greatly contribute to resolving these issues. If people who have been plagued by poverty and conflict become prosperous and have the opportunity for education, many talented individuals who were previously overlooked will emerge from these regions and contribute to the further development of humanity. There is a saying from Guan Zhong, a chancellor of the state of Qi during the Spring and Autumn period: "When the granaries are full, they will know propriety and moderation; when their clothing and food are adequate, they will know the distinction between honor and shame." Regardless of the causal relationship between money and character, there is no doubt that prosperity can greatly advance humanity.

The realization of a prosperous and peaceful world supported by a global energy supply... Room-temperature superconductivity holds the potential to revolutionize human society. As long as the possibility of room-temperature superconductivity exists, am I the only one who thinks the future of humanity is still full of hope? I hope that among the young people reading this while thinking about their future, many will emerge who are determined to realize this "mega-project" with their own hands.

But one word of caution: if you don't hurry, I might just achieve room-temperature superconductivity myself. What? You want a hint for achieving room-temperature superconductivity? That's a secret!

Postscript

Just as I was writing this, it was reported in the news that the development of next-generation automobiles using superconducting motors and power transmission experiments using existing superconducting cables were entering their final stages. A new era may be just around the corner.