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Spinons and Holons
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Holons (also known as chargons, from English hole or charge, plus the -on prefix for particles) are one of three quasiparticles, along with spinons and orbitons, that electrons in solids are able to split into during the process of spin-charge separation, when extremely tightly confined at temperatures close to absolute zero.
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The theory has been around for more than 40 years, but only now has it been confirmed through direct and unambiguous experimental results. Working at the Advanced Light Source (ALS) of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory, a team of researchers has observed the theoretical prediction of electron “spin-charge separation” in a one-dimensional solid. These results hold implications for future developments in several key areas of advanced technology, including high-temperature superconductors, nanowires and spintronics.

Just as the body and wheels of a car are thought to be intrinsic parts of a whole, incapable of separate and independent actions, i.e., the body goes right while the wheels go left, so, too, are electrical charge and spin intrinsic components of an electron. Except, according to theory, in one-dimensional solids, where the collective excitation of a system of electrons can lead to the emergence of two new particles called “spinons” and “holons.” A spinon carries information about an electron’s spin and a holon carries information about its charge, and they do so as separate and independent entities. Numerous experiments have tried to confirm the creation of spinons and holons, referred to as spin-charge separation, but it took the technological advantages offered at ALS Beamline 7.0.1, also known as the Electronic Structure Factory (ESF), to achieve success.

In a paper published in the June 2006 issue of the journal Nature-Physics, researchers have reported the observation of distinct spinon and holon spectral signals in one-dimensional samples of copper oxide, SrCuO2, using the technique known as ARPES, for angle-resolved photoemission spectroscopy. The research was led by Changyoung Kim, at Yonsei University, in Seoul, Korea, ALS scientist Eli Rotenberg, and Zhi-Xun Shen of Stanford University, a leading authority on the use of ARPES technology. Co-authoring the Nature-Physics paper with them were Bum Joon Kim and Hoon Koh, plus S.J. Oh, H. Eisaki, N. Motoyama, S. Uchida, T. Tohyama, and S. Maekawa.


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