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China's top 10 S&T news stories in 2005: Controlling the Kondo effect of an adsorbed magnetic ion through its chemical bonding

With the aid of low-temperature ultra-high vacuum scanning tunneling microscopy, a research team from the University of Science and Technology of China carried out a delicate single-molecule manipulation on cobalt pigment element (cobalt phthlocyanine, CoPc), hence realizing the control over the magnetic state of a single molecule. For the first time in the world, they induced chemical reactions inside a single molecule, changing and controlling the physical properties in the molecule by making use of selective chemical reactions. The success provides a new and important approach for the development of single molecular devices and opens new horizons for future development of the subject. The development was reported in the journal Science.

Controlling the Kondo Effect of an Adsorbed Magnetic Ion Through Its Chemical Bonding

Science 2 September 2005: Vol. 309 no. 5740 pp. 1542-1544 DOI: 10.1126/science.1113449

We report that the Kondo effect exerted by a magnetic ion depends on its chemical environment. A cobalt phthalocyanine molecule adsorbed on an Au(111) surface exhibited no Kondo effect. Cutting away eight hydrogen atoms from the molecule with voltage pulses from a scanning tunneling microscope tip allowed the four orbitals of this molecule to chemically bond to the gold substrate. The localized spin was recovered in this artificial molecular structure, and a clear Kondo resonance was observed near the Fermi surface. We attribute the high Kondo temperature (more than 200 kelvin) to the small on-site Coulomb repulsion and the large half-width of the hybridized d-level.

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