Mysterious force found behind strange superconductor metals

3 Aug 2018

Levitating magnet on a superconductor. Image: Dmitry Veselov/Shutterstock

Scientists analysing a group of truly strange metals have found a whole new superconductor capability.

Metals known as cuprates have fascinated scientists for their strange characteristics, but a recent discovery published in Science has found that they also carry current in a completely different way to other metals such as copper.

Cuprates are high-temperature superconductors (HTS), which means that they can carry electric current without any loss compared to low-temperature superconductors (LTS).

However, while scientists have grasped the physics of LTS, there is still much to be learned about HTS, specifically how the electrons travel through these materials.

In conventional metals, electricity can travel through them as units known as quasiparticles, which act almost independently of each other.

‘A new way metals can conduct electricity’

Wondering whether this phenomenon can help explain HTS, a team from Florida State University looked at one specific cuprate called lanthanum strontium copper oxide (LSCO).

When the temperature is low enough, its normal, superconducting metallic state emerges, but is referred to as a ‘strange’ or ‘bad’ metal because the electrons don’t conduct electricity very well. When placed in a very high magnetic field with a current running through it, however, it returned some truly unexpected results.

The resulting data revealed that the current cannot, in fact, travel via conventional quasiparticles, as it does in copper or doped silicon.

“This is a new way metals can conduct electricity that is not a bunch of quasiparticles flying around, which is the only well-understood and agreed-upon language so far,” said Arkady Shekhter, who led the research. “Most metals work like that.”

As for what could be carrying the charge through LSCO, the team decided to test it within a very powerful magnet – nearly 30 times more powerful than a hospital MRI machine – to find its resistivity.

What became apparent was that LSCO not only carries quasiparticles when it is conducting electricity, but some other mysterious force.

“Here we have a situation where no existing language can help,” Shekhter said. “We need to find a new language to think about these materials.”

Colm Gorey was a senior journalist with Silicon Republic