Spin-orbital separation observed in a Mott insulator
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Spin-orbital separation observed in a Mott insulator
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lectrons in atoms can be described by three quantum numbers: spin, charge, and orbital. In an experiment performed at the Paul Scherrer Institute in Switzerland, these properties have now been separated. In one-dimensional systems, it is predicted that the electrons can separate into independent quasi-particles, which cannot leave the material in which they have been produced. While quasi-particles carrying either spin (spinons) or charge (holons or chargons) have already been identified, an international team of researchers led by experimental physicists from the Paul Scherrer Institute, Switzerland, and theoretical physicists from the IFW Dresden, Germany, have now succeeded in separating quasi-particles carrying the orbital degree of freedom (orbitons). These results are reported in the May 3 issue of Nature (DOI: 10.1038/na-
Nano Focus X-ray microscope captures nanoscale structures in 3D
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new x-ray microscope probes the internal structures of materials smaller than human cells and creates unparalleled high-resolution, three-dimensional (3D) images. By integrating unique automatic calibrations, scientists at Brookhaven National Laboratory are able to capture and combine thousands of images with greater speed and precision
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MRS BULLETIN
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VOLUME 37 • JUNE 2012
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als and geometries by making modifications to the key parameters in the dielectric function. The research team now anticipates that researchers may be able to exploit the behavior of quantum-sized nanoparticles for a variety of applications. Because of their high-surface-area-tovolume ratios, these nanoparticles are ideal candidates for sensor and catalysis
applications, particularly for events that involve interactions with very few photons or transferred electrons. Quantumsized nanoparticles may also be of value in biological systems since they should be able to maneuver through cellular environments with greater ease than their larger counterparts. Anthony S. Stender
ture10974; p. 82). The electron’s breakup into two new particles—spinons and orbitons—has been gleaned from measurements on the copper-oxide compound Sr2CuO3, a onedimensional Mott insulator. This material has the distinguishing feature that the particles in it are constrained to move in one direction only, either forward or backward. Using x-rays, scientists have lifted some of the electrons belonging to the copper atoms in Sr2CuO3 to orbitals of higher energy, corresponding to the motion of the electron around the nucleus with higher velocity. 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, ” said Thorsten Schmitt, head of the experimental team, “but also extremely
high-precision x-ray detectors.” “It had been known for some time that, in part
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