How does hydrogen enhance superconductivity?
Researchers have been looking at hydrogen-rich materials for a long time. According to theoretical predictions, lattice vibrations play a major role in high-temperature superconductivity. The faster the atoms vibrate and the stronger these vibrations are with the electrons in the material, the greater the critical temperature above which electricity can flow without loss. And hydrogen, as the lightest of the elements, not only has the highest vibration frequency — vibrations known as phonons are also strongly coupled to electrons.
It has long been known that pure hydrogen will become superconducting at room temperature. The crux of the matter: The required metallic hydrogen forms only at a pressure of more than 500 gigapascals, five million times the atmospheric pressure. The situation is somewhat better for materials in which hydrogen is bonded to other elements. In 2015, a working group found out sulfur hydride h3S becomes superconducting at 203 K – Only 70 degrees Celsius below the freezing point of water, but still at a pressure of 155 gigapascals.
These are worlds far from the first superconductors near absolute zero. However, the fact that temperatures are increasingly approaching technically achievable values has been purchased at the expense of the fact that the necessary pressures are now absurdly high. Experts are now looking for ways to reverse this trend. Yesterday they were high-temperature superconductors – today we’re chasing low-pressure superconductors.
Similar to high transition temperatures, a new class of materials raises hopes here, too: ternary hydrides. With them, a third, mostly light component is added to the hydrate. This improves the stability of the hydrogen-rich crystal lattice so that materials formed in this way remain stable even at low pressures. In addition, the simulations show that a third element can increase the transition temperature of the hydrides.
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