Physicists observe the splitting of an electron
An electron has been observed to decay into two separate particles, each carrying a particular property of the electron: a spinon carrying its spin – which makes an electron akin to a tiny magnet – and an orbiton carrying its orbital moment, which arises from the electron's motion around a nucleus. These newly created particles are confined to the material in which they are produced. This result is reported in a paper published in Nature by an international team of experimental and theoretical physicists, including former FOM project leaders Prof.dr. Jean-Sébastien Caux and Prof.dr. Jeroen van den Brink.
Electrons are fundamental particles whose characteristics include electric charge and 'spin', the latter meaning that they can be viewed as tiny magnets eventually giving rise to magnetism in materials. In fact, electrons in a material possess another characteristic called 'orbital', representing the paths which electrons follow when orbiting nuclei. Usually, spin and orbital properties are bound to an individual electron. In an experiment performed at the Paul Scherrer Institute, these properties have now been separated.
X-rays split the electron into spinon and orbiton
The electron's breaking up into two new particles is 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 forward or backward. Using x-rays, the scientists lifted some of the electrons belonging to the copper atoms in Sr2CuO3 to orbitals of higher energy, corresponding to motion of the electron further away from the nucleus. After being excited with x-rays, the electronic degrees of freedom split into two parts. One of the new particles created, the spinon, carries the electron’s spin while the other one, the orbiton, carries its extra orbital energy. This study offers the first observation of the spin and orbital degrees of freedom actually breaking away and separating from each other.
In the experiment, high energy 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 physicists can trace the properties of the newly produced particles. "These experiments not only require very intense x-rays with an extremely well-defined wave length to interact with 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 world-leading at the moment."
Electron splitting could be found in many other materials
The theory team, led by FOM project leaders Jeroen van den Brink (IFW Dresden, Germany) and Jean-Sébastien Caux (IoP, University of Amsterdam), has provided the theoretical interpretation of the results. "It had been known for some time that in particular materials an electron can in principle be split", says van den Brink, "but until now the empirical evidence for the existence of spinons and orbitons was lacking." The interpretation of the experimental data has been made possible by detailed state-of-the-art theoretical predictions for the spin response of the material, obtained by Caux at the University of Amsterdam. Says van den Brink: "Now that we know where exactly to look for them, we are bound to find these new particles in many more materials."
Results may help understand high temperature superconductivity
The observation of electron separation may also have important implications in the search for high temperature superconductors. Due to the similarities in the behaviour of electrons in Sr2CuO3 and copper-based superconductors, understanding the principles behind this electron splitting would provide input for theories trying to explain the phenomenon of high-temperature superconductivity.
Contact
Dr. Thorsten Schmitt (experiments)
Paul Scherrer Institut, Switzerland
Tel: +41 56 310 37 62
Prof.dr. Jeroen van den Brink (theory)
IFW Dresden, Germany
Tel: +49 351 4659 400
Prof.dr. Jean-Sébastien Caux
IoP, University of Amsterdam, The Netherlands
Reference
'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.