Swiss, German physicists split the electron

Spin here, orbit there

By Richard Chirgwin, 19th April 2012

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An international research team has observed an electron being split into two “quasi particles”, one carrying the original particle’s spin, the other carrying its orbital movement.

Spin (giving rise to magnetism) and angular momentum (the path the electron follows around the nucleus of an atom) are two out of the electron’s three quantum properties (the other is charge). These properties attach to a single electron – unless, it seems, you pump the right substance with the right amount of energy.

The material is Sr₂CuO₃ – strontium and copper oxide – and the energy was delivered by X-rays from the Swiss Light Source. A comparison of the energy and momentum of the X-rays before and after collision with the material allowed the properties of the newly-created quasi-particles to be traced.

What the Paul Scherrer Institute researchers found in the traces was that the excited electrons split into a spinon, containing the spin of the original electron, and an orbiton, which carried the electron’s orbital energy.

According to Physorg, “the fundamental spin and orbital moments have been observed, for the first time, to separate from each other.”

In their paper in Nature (abstract), the research team says “We resolve an orbiton separating itself from spinons and propagating through the lattice as a distinct quasi-particle with a substantial dispersion in energy over momentum, of about 0.2 electronvolt”.

While the separation of spin from angular momentum has not been observed before, the separation of spin (spinons) from charge (holons) was first observed 15 years ago, the researchers state in their paper.

The researchers say their work will help understand the properties of high-temperature superconductors, because electrons in Sr₂CuO₃ behave similarly to those in copper-based superconductors. ®

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