One of the disctinctive features of superconductivity is that any superconducting material will expel magentic fields, causing magnets to levitate over suitable materials when carrying currents, a technology engineers are keen to use to make frictionless trains. University of Rochester photo / J. Adam Fenster
One of the holy grails of physics research has been reached, but it's not yet everything we've been hoping for. A material has been engineered that conducts electricity with zero resistance at room temperature. Unfortunately, it also requires unimaginably high pressures.
Until 1911, it was believed that all substances resist the passage of electricity, with some turning to heat. The resistance of most materials falls with temperature, but the discovery that for some it suddenly drops to zero, known as superconductivity, in conditions of extreme cold was a shock.
In 1986, the physics world was rocked again with the discovery that certain ceramics become superconducting at high temperatures, a finding rewarded with one of the quickest Nobel Prizes in Physics in history the following year. However, “high temperature” in this field doesn't mean what you might think; anything above -196.2°C(-321.1°F), the boiling point of nitrogen, qualifies.
For 34 years, scientists have edged ever closer to the goal of superconductors at temperatures that won't give you frostbite. Now Dr Ranga Dias of the University of Rochester has done just that. However, like the heroes of many quests that seek the mythical grail, what he has found doesn't quite match the dream.
In Nature, Dias describes using pressures of 39 million pounds per square inch and hours of laser pulses to infuse hydrogen into equal quantities of carbon and sulfur to make a material that superconducts at 15°C (59°F). Unfortunately, that's 2.5 million times the atmospheric pressure at sea level, something that can only be achieved by squeezing minute quantities of the material between two diamonds.
Robust superconductivity under everyday conditions would unleash a string of technologies that would likely change our world more than almost any other scientific breakthrough. Electricity could be stored or transmitted great distances for almost no cost, for example. The distinctive magnetic fields superconductors create would be game-changers for scientific instruments, medical imaging devices, and frictionless transport devices. For this to occur, however, we not only need vastly larger quantities than Dias' technique offers but we also need realistic pressures.
Dias thinks such achievements are on their way. “Because of the limits of low temperature, materials with such extraordinary properties have not quite transformed the world in the way that many might have imagined. However, our discovery will break down these barriers and open the door to many potential applications," he said in a statement.
Encouragingly, Dias's superconductors don't require rare or expensive components. "To have a high-temperature superconductor, you want stronger bonds and light elements. Those are the two very basic criteria," Dias said. "Hydrogen is the lightest material, and the hydrogen bond is one of the strongest.”
Helpfully, it is also the most common element in the universe, and carbon and sulfur are also abundant.
The formation of metallic hydrogen at very high pressures was proposed by astronomers to explain otherwise puzzling observations of Jupiter, and it was manufactured in the lab in 2017. Dias saw the potential of using hydrogen-rich organic materials, rather than pure hydrogen, providing opportunities for what he calls “compositional tuning” to achieve superconductivity in easier to achieve conditions.
