Truly weird superconductor is actually a whole lot stranger than we thought

21 Mar 2018

Superconductive materials such as strontium titanate have the strange ability to levitate magnets when a current is flowing through them. Image: ktsdesign/Shutterstock

A material that has baffled scientists for decades because of its superconductive ability has been analysed in detail, showing it to be even stranger still.

When it comes to weird science, superconductive materials are definitely on the stranger side, thanks to their ability to allow an electric current to flow through them with 100pc efficiency and no resistance.

Until around 50 years ago, it was thought that the only superconductors were metals because they have the largest number of loosely bound ‘carrier’ electrons, but then along came a material called strontium titanate that threw out the rulebook.

Now, a team of scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University has documented its latest research into the material, revealing something that is significantly weirder than we ever thought.

Categorised as ‘unconventional’ because it can’t be explained by existing theories, strontium titanate is effectively at the other end of the spectrum when it comes to the density of available electrons of any known superconductor.

What defines unconventional?

In what could be considered a traditional superconductor, its ability is triggered by natural vibrations that ripple through a material’s atomic latticework.

The vibrations cause carrier electrons to pair up and condense into a superfluid, which flows through the material with no resistance.

But when we enter into the unconventional territory of strontium titanate, there is currently no scientific understanding as to what glues the electron pairs together.

In order to see the behaviour of superconductors down at an atomic level, researchers would need to use tunnelling spectroscopy, which, for the past several years, has not been achievable.

But now, in what is the first complete set of data to come from analysis, the findings show that strontium titanate is the exact opposite of what you’d expect in a superconductor in that its lattice vibrations are strong and its carrier electrons are few and slow.

‘Everything is upside down’

As one of the investigators, Harold Hwang, puts it: “This is a system where everything is upside down.”

Interestingly, the team added that details such as the behaviour and density of the electrons, and the energy required to form the superconducting state, match what you would expect from conventional superconductivity theory almost exactly.

Adrian Swartz, who led the experiment, clarified: “Strontium titanate seems to be an unconventional superconductor that acts like a conventional one in some respects.

“This is quite a conundrum, and quite a surprise to us. We discovered something that was more confusing than we originally thought, which, from a fundamental physics point of view, is more profound.”

He added: “If we can improve our understanding of superconductivity in this puzzling set of circumstances, we could potentially learn how to harvest the ingredients for realising superconductivity at higher temperatures.”

Colm Gorey was a senior journalist with Silicon Republic