Electrons doing the splits

April 18, 2012, Paul Scherrer Institute
Artist's impression of an electron splitting up into two new particles: a spinon carrying the electron's spin and an orbiton carrying its orbital moment. (Graphics: David Hilf, Hamburg)

Observations of a 'single' electron apparently splitting into two independent entities -- so-called quasi-particles -- are reported in this week’s Nature.

An electron has been observed to decay into two separate parts, each carrying a particular property of the electron: a spinon carrying its spin - the property making the electron behave as a tiny compass needle - and an orbiton carrying its orbital moment - which arises from the electron's motion around the nucleus. These newly created particles, however, cannot leave the material in which they have been produced. This result is reported in a paper published in Nature by an international team of researchers led by experimental physicists from the Paul Scherrer Institute (Switzerland) and theoretical physicists from the IFW Dresden (Germany).

All electrons have a property called "spin", which can be viewed as the presence of tiny magnets at the atomic scale and which thereby gives rise to the magnetism of materials. In addition to this, electrons orbit around the atomic nuclei along certain paths, the so-called electronic "orbitals". Usually, both of these quantum physical properties (spin and orbital) are attached to each particular electron. In an experiment performed at the Paul Scherrer Institute, these properties have now been separated.

The electron's break-up into two new particles has been gleaned from measurements on the copper-oxide compound Sr2CuO3. This material has the distinguishing feature that the particles in it are constrained to move only in one direction, either forwards or backwards. Using X-rays, scientists have lifted some of the electrons belonging to the copper atoms in Sr2CuO3 to orbitals of higher energy, corresponding to motion of the electron around the nucleus with higher velocity. After this stimulation with X-rays, the electrons split into two parts. One of the new particles created, the spinon, carries the electron's spin and the other, the orbiton, the increased orbital energy. In this study, the fundamental spin and orbital moments have been observed, for the first time, to separate from each other.

In the experiment, X-rays from the Swiss Light Source (SLS) are fired at Sr2CuO3. By comparing the properties (energy and momentum) of the X-rays before and after the collision with the material, the properties of the newly produced particles can be traced. "These experiments not only require very intense X-rays, with an extremely well-defined energy, to have an effect on the electrons of the copper atoms", says Thorsten Schmitt, head of the experimental team, "but also extremely high-precision X-ray detectors. In this respect, the SLS at the Paul Scherrer Institute is leading the world at the moment."

"It had been known for some time that, in particular materials, an electron can in principle be split", says Jeroen van den Brink, who leads the theory team at the IFW Dresden, "but until now the empirical evidence for this separation into independent spinons and orbitons was lacking. Now that we know where exactly to look for them, we are bound to find these new particles in many more materials."

Observation of the electron splitting apart may also have important implications for another current research field - that of high-temperature superconductivity. Due to the similarities in the behaviour of electrons in Sr2CuO3 and in copper-based superconductors, understanding the way decay into other types of in these systems might offer new pathways towards improving our theoretical understanding of high-temperature superconductivity.

Explore further: New ways to tune electrical conductivity revealed by electron interaction

More information: Spin-Orbital Separation in the quasi 1D Mott-insulator Sr2CuO3, J. Schlappa, K. Wohlfeld, K. J. Zhou, M. Mourigal, M. W. Haverkort, V. N. Strocov, L. Hozoi, C. Monney, S. Nishimoto, S. Singh, A. Revcolevschi, J.-S. Caux, L. Patthey, H. M. Rønnow, J. van den Brink, and T. Schmitt; Nature, Advance Online Publication, 18.04.2012, DOI: 10.1038/nature10974

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2.5 / 5 (4) Apr 18, 2012
Perhaps it's semantics, but if you can "split" a particle, then that's two particles how can you have a quasi-particle? Yes, I know it says in the article that the spinon and orbiton cannot leave the material in which they are produced but what if that material is spread out over macroscopic distances? Does it mean only certain kinds of material, or could that extend to space, if space is really filled with dark matter and energy? Could it happen in a Bose-Einstein condensate?
5 / 5 (2) Apr 18, 2012
Perhaps it's semantics, but if you can "split" a particle, then that's two particles how can you have a quasi-particle?

Like splitting photons for quantum entanglement to make two quasi-photons? Common words to describe quantum mechanics is many times not intuitive.
3.7 / 5 (3) Apr 18, 2012

Like splitting photons for quantum entanglement to make two quasi-photons? Common words to describe quantum mechanics is many times not intuitive.

Yeah, but splitting photons for entanglement creates two photons, not quasi photons.
4.5 / 5 (6) Apr 18, 2012
Yeah, but splitting photons for entanglement creates two photons, not quasi photons.

Not really. They are single system even when separated by large distance which is why action at distance is so 'spooky'.
Short bloke
not rated yet Apr 20, 2012
Hard X rays are produced by impacting high velocity electrons, the X ray resulting from a proportion of the electron mass and impact target mass phase changing to a jet of energy. Impact of such a high velocity energy jet with an electron would become part of the debris that could spin off in any direction.
5 / 5 (3) Apr 20, 2012
if you can "split" a particle, then that's two particles how can you have a quasi-particle?
Quasi-particles ( http://en.wikiped...particle ) are not fundamental particles.

The process being described in this article starts with the excitation of an electron by an x-ray photon. When this electron transitions to a different state that has less orbital angular momentum and different spin some other electron has to take up the difference (in order to conserve total angular momentum = orbital angular momentum spin). It so happens that different electrons can take on the spin and orbital angular momentum. These properties can be exchanged from an electron in one atom to one in another, i.e. they propagate. Due to quantum mechanics these properties can only change in discrete amounts; so these properties propagate like (quantum mechanical) particles. This sort of phenomenon (propagating changes in properties) is common in solid state and condensed matter physics.
1 / 5 (1) Apr 20, 2012
In nuclear physics the internal degrees of particle motion are called the "colors" and what this experiment does is essentially a color chromatography of electron: the degrees of electron motion (rolling and spinning motion) are washed across lattice of Mott's insulator, along which they do spread in different speed, thus manifesting itself as a distinguished quasiparticles.
not rated yet Apr 21, 2012
funny i always thought of spin as the particles angular momentum -- ahh well
not rated yet Apr 22, 2012
total angular momentum = orbital angular momentum spin
That should be: total angular momentum = orbital angular momentum plus spin.

i always thought of spin as the particles angular momentum
It is, in the sense that spin does not require the presence of other particles (unlike orbital angular momentum which requires something for the particle to "orbit"). Though it is different from ordinary (classical) angular momentum in that fundamental particles can have it.

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