Big mystery holding back practical superconductors may have been solvedS

Superconductors carry electric current with no energy loss. They could revolutionize our electrical grid, but they only work at impractically low temperatures. We just figured out a key reason why – and possibly got a lot closer to room-temperature superconductors.

Scientists have spent the last two decades trying to figure out why their superconductors only work at temperatures barely any higher than absolute zero. They've been able to identify the so-called "pseudogap" phase, which is a temperature range below room temperature at which superconductivity breaks down. We know there's something about what happens to electrons during this phase that makes superconductors fail, but until now we couldn't figure out what, despite several frustrating attempts to find out.

But physicists working for the Department of Energy may have just solved the mystery. Working with copper-oxide superconductors, they identified a change in electron behavior that only occurs during the pseudogap phase. Specifically, they keyed in on how easily electrons could "jump" from each copper and oxygen site to the tip of a microscope needle.

The difference in electron behavior was remarkably obvious, explains project leader Séamus Davis:

"Picture the copper atom at the center of the unit, with one oxygen to the 'north' and one to the 'east,' and this whole unit repeating itself over and over across the copper-oxide layer. In every single copper-oxide unit, the tunneling ability of electrons from the northern oxygen atom was different from that of the eastern oxygen."

Finding such a clear break in symmetry is very exciting, because there's a ton of precedent for such asymmetries revolutionizing our understanding of other systems. For instance, the discovery of broken symmetries in liquid crystals gave scientists the guidance needed to control the crystal, and now liquid crystal displays (or, as they're more commonly known, LCD screens) are commonplace and inexpensive. The hope is that a similarly huge leap in understanding of superconductors will come from uncovering this asymmetry in the pseudogap phase.

The researchers hope to find similar broken symmetries in other copper-oxide superconductors. They are also trying to figure out how the asymmetry affects electron flow, how this in turn affects superconductivity, and how to work around these issues to make room temperature superconductors a practical possibility.

There's still much work to do, but as Davis explains, the potential benefits are incalculable:

"Developing superconductors that operate without the need for coolants would be transformational. Such materials would greatly improve the efficiency of energy-distribution systems, saving enormous amounts of money and updating the electrical grid to meet the needs of the 21st Century."

Currently, the only working superconductors have to operate at extremely low temperatures. The fact that they operate with no resistance and thus no energy loss is theoretically a huge savings, but in practice it's completely canceled out by the huge amount of exotic coolants needed to get them to such temperatures.

[Nature]

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