A sample of lanthanum hydride has passed two of the three tests for superconductivity at -23ºC (-9ºF). Easily the highest temperatures at which we have found such strong signs of zero electrical resistance. This is the first time we have observed this phenomenon at temperatures that happen frequently on Earth naturally. However, the phenomenal pressures required mean this is still very much a laboratory phenomenon.
To distinguish superconductivity from ordinary very low resistance, scientists measure the loss of current from a loop with time. They also look for a fall in the temperature where resistance appears to vanish when a magnetic field is applied, and the capacity to expel magnetic fields. In December 2018 a preprint of a paper created a buzz by claiming to have achieved the first two of these at temperatures typical during northern nations’ winters.
After passing peer review, that work has now been published in Nature. Although this improves confidence the claims are real, true confirmation requires the third test, which is unlikely to be possible with this experimental set-up.
Following the announcement that hydrogen sulfide becomes superconducting at temperatures of -70º C (-94º F) and enormous pressures, A. P. Drozdov of the Max Plank Institute placed a sample of lanthanum hydride inside a metal foil, surrounded it with hydrogen, and squeezed it between two diamonds. With pressures of 1.6 million times the atmosphere at sea level (half that at the center of the Earth), resistance was either zero or too low to measure, and the anticipated temperature drop was observed.
Unfortunately, with a sample size of just 0.01 millimeter across (0.0004 inches), it’s impossible to detect if magnetic fields were expelled.
The idea that, under sufficient pressure, elements with low atomic mass would be super-conducting at almost ambient temperatures, was predicted in 2004. As the lightest element, hydrogen, and molecules rich in it, was the obvious target to study. When Drozdov replaced the ordinary hydrogen with the isotope deuterium, which has an extra neutron, lower temperatures were required for zero resistance, just as anticipated.
When the phenomenon of superconductivity was discovered in 1911 it fascinated physicists, but practical uses were limited by the fact it only occurred at temperatures close to absolute zero. Removing that much heat required very expensive liquid helium.
After decades of painfully slow increases in the highest temperature at which superconductivity was observed a dramatic increase was announced in 1986, allowing cooling with much cheaper liquid nitrogen.
The dream is to require no cooling at all. Among other technological wonders, electricity could be conducted with zero loss across the planet. To do that, however, we’ll have to achieve the phenomenon not only at room temperature, but at modest pressures, and that still looks to be a long way off.