Science & Environment

Electron 'split-personality' seen in new quasi-particle

Copper oxide "chain" for quasiparticle experiments
Image caption The structure of the material permits careful study of electrons as they only have one way to move in it

Researchers have discovered another way that electrons - one of the Universe's few fundamental particles - can undergo an "identity crisis".

Electrons can divide into "quasi-particles", in which their fundamental properties can split up and move around like independent particles.

Two such quasi-particles had been seen before, but a team reporting in Nature has now confirmed a third: the orbiton.

These orbitons carry the energy of an electron's orbit around a nucleus.

Generally, these properties are not independent - a given electron has that set of properties, maintaining them as it moves around, while a nearby electron has a different set.

But the idea of quasi-particles allow these properties to split and move around independently, granting them to nearby electrons.

An analogy of this slippery idea is a traffic jam on a one-lane road - it is as if one blue car, pointed west and running at 1,000 RPM, passes on its blueness, its engine speed and its direction to adjacent cars.

The cases in which such strange behaviour can be induced are rare, but an international team of researchers turned to a material called strontium cuprate to investigate it.

Image caption Electrons can be bumped up and down into different "orbits" around their host nucleus

The arrangement of atoms in the material is much like the one-lane road: electrons can only move in one direction along it in what is called a spin chain.

The team used the Swiss Light Source at the Paul Scherrer Institut in Switzerland to shine intense X-ray beams into the material, catching the light that came out with precision detectors.

Analysis of how the X-ray beam was altered in the process gave evidence of how electrons were given an energy boost, and where it went.

Thorsten Schmitt of the Swiss Light Source explained that the team made an unexpected find.

They saw that some of the X-ray energy went into raising an electron to a different orbit around a nucleus, and that this "orbital excitation" could move along the chain, bumping an adjacent electron up an orbit, and then the next electron along, and so on.

"We wanted to understand the spinon excitations - we were sure we would see spinons - the surprise was also to get these orbital excitations behaving in a collective way," he told BBC News.

It is a find destined for fundamental physics textbooks, but Dr Schmitt says that the curious behaviour may help scientists understand equally curious effects in similar materials.

"It's all basic research but we hope this is very relevant for understanding superconductivity in cuprates, which are made out of the same building blocks."

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