High-temperature superconductivity helps scientists measure small magnetic fields, and aids advances in fields including geophysical exploration, medical diagnostics and magnetically levitated transportation. The discovery earned Bednorz and Müller the 1987 Nobel Prize in Physics. Credit: IBM.

High-temperature superconductivity helps scientists measure small magnetic fields, and aids advances in fields including geophysical exploration, medical diagnostics and magnetically levitated transportation. The discovery earned Bednorz and Müller the 1987 Nobel Prize in Physics. Credit: IBM.

Scientists in Germany claimed that they have achieved superconductivity at 250 K, or –23 °C — about the average temperature found at the North Pole. The new record brings us closer to achieving superconductivity (zero electrical resistance) at room temperature, which would revolutionize the way we generate energy, transfer data, or build computers.

You can’t resist progress

Superconductivity was first discovered by Dutch Physicist Heike Kamerlingh Onnes in 1911, when he and his students found that the electrical resistance of a mercury wire, cooled to about 3.6 degrees above absolute zero, made a dramatic plunge. The drop was enormous – the resistance became at least twenty thousand times smaller than at room temperature. Ever since then, scientists have struggled to understand this peculiar state — but there has been very good progress.

For instance, we know superconductivity is a quantum mechanical phenomenon characterized by the Meissner effect – the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state.

The most common superconductors typically have to be cooled down with liquid nitrogen close to -250°C (-480°F) for them to conduct electricity with no resistance. In this state, the conductor is comprised of a rigid lattice of positive ions drowned in a sea of electrons.

A normal conductor has electrical resistance because electrons moving through the lattice also bump into it, slowing down in the process. This motion also causes atoms to vibrate, which is why electrical resistivity also leads to heat loss.

On the other hand, in a superconductor, the lattice is so rigid due to the low temperature that mechanical sound waves (phonons) ripple through it — and electrons ride the wide along with them. What’s more, electrons in a superconductor form bonds called ‘Cooper pairs’. When the temperature rises, the Cooper pairs break apart and the superconductive state dissolves.

In 2014, researchers at the Max Planck Institute for the Structure and Dynamics of Matter were able to achieve superconductivity at –80°C, using hydrogen sulfide. The next year, the record was broken again at –70 °C. Now, Mikhail Eremets and colleagues at the Max Planck Institute for Chemistry in Germany have raised the bar even higher — they’ve achieved superconductivity at right about the average temperature of the North Pole. That’s extremely close to the ultimate goal of achieving room temperature superconductivity that would enable new electrical highways or a new generation of supercomputers, among many other things. Just four years ago, the record temperature for superconductivity was –230 °C.

Credit: Mikhail Eremets et al.

Credit: Mikhail Eremets et al.

Eremets and colleagues worked once more with hydrogen sulfide, whose atoms were firmly pressed between diamond anvil cells, subjecting them to a huge pressure of 170 gigapascals, or half that found at the center of the Earth.

“This leap, by ~ 50 K, from the previous record of 203 K indicates the real possibility of achieving room temperature superconductivity (that is at 273 K) in the near future at high pressures,” say Eremets and co.

According to MIT Technology Review, the German physicists still have to provide more evidence that the superconductivity they claimed to have reached is genuine. One obvious problem encountered thus far is the fact that hydrogen sulfide atoms do not expel a magnetic field (evidence of the Meissner effect). But this may be more of a measurement problem because the samples that the researchers worked with were in the order of micrometers.

In the meantime, there are reasons to believe that superconductivity can be reached at an even higher critical temperature. For instance, computational models suggest that yttrium superhydrides could superconduct at a cozy 27°C but at a huge pressure akin to that found at the center of the planet.

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