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Pictured: A superconducting hoverboard
Superconducting materials are widely used in our daily lives. Examples include aluminum, calcium, tin, and lead. Even some non-metallic elements like silicon, sulfur, and phosphorus can become superconductors under high pressure.
The science fiction movie "Avatar" not only gave us stunning 3D visuals but also introduced us to the beautiful and magical world of Pandora. One of the most unforgettable scenes is the floating Hallelujah Mountains, drifting above the clouds, covered in thick vines, with waterfalls hanging from the cliffs and strange birds flying around. These mountains seem to float effortlessly in the sky.
What kind of mysterious force allows such massive mountains to stay suspended? According to the movie, it's due to a rare material called "Unobtanium," which is a room-temperature superconductor. Using powerful magnetic fields near the mother tree, this material helps keep the mountains floating. This fictional resource has driven humans to destroy the Na’vi people’s homes in their quest for wealth.
So what exactly is a superconducting material? Why is it so effective at magnetic levitation? And is there a room-temperature superconductor on Earth today?
The Power of Superconductivity
A Superconductive Board Can Lift Sumo Wrestlers
Superconductivity means that a material can conduct electricity without resistance. When cooled below its critical temperature, a superconductor loses all electrical resistance, allowing current to flow indefinitely without any loss. If placed in a magnetic field, it generates an opposing field that cancels out the external one, making it completely diamagnetic. This property is key to magnetic levitation.
The interaction between the superconductor and the magnetic field creates a repulsive force strong enough to lift heavy objects. In fact, a small superconducting plate can easily lift a sumo wrestler. This principle is used in experimental maglev systems, where superconductors float above magnets, creating stable, frictionless motion.
Superconducting Conditions
Critical Temperature Is Very Low
Although superconductivity is common in many materials, achieving it requires cooling them to very low temperatures. For example, mercury, the first known superconductor, works at just 4K (-269°C). Most metals and alloys have even lower critical temperatures, making real-world applications difficult. Liquid helium is often needed to cool them, which is expensive and impractical for everyday use.
A Prediction That Misled Researchers
In 1957, physicists Bardeen, Cooper, and Schrieffer proposed a theory explaining superconductivity in conventional materials. They predicted that the maximum critical temperature would be around 40K, which led scientists to believe that higher-temperature superconductors were unlikely. However, this belief was soon challenged by new discoveries.
Hope in Superconductivity
The Growing Family of High-Temperature Superconductors
Despite the initial limitations, researchers kept searching for better materials. In 1986, Böchler and Müller discovered a ceramic compound with a critical temperature of 35K. Later, Chinese scientists found materials with critical temperatures as high as 93K. These materials, now known as high-temperature superconductors, operate in the liquid nitrogen temperature range, significantly reducing costs.
Today, superconductors come in many forms, from metals and oxides to organic compounds. Scientists continue to explore new materials, such as iron-based superconductors and magnesium diboride. Each discovery brings us closer to the dream of room-temperature superconductivity.
Theoretical predictions suggest that hydrogen might become a superconductor at room temperature under extreme pressure. While still in the experimental stage, this could revolutionize energy transmission, transportation, and more.
Imagine a future where you can float in the clouds or sleep on a levitating sofa. With continued research, this may one day become reality. (Wen Luohui) – A Ph.D. in Physics from the Chinese Academy of Sciences, specializing in neutron scattering studies of high-temperature superconductors.
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