A team of scientists including researchers from the London Centre for Nanotechnology at UCL (University College London) and the IBM Almaden Research Center has forged a breakthrough in understanding an intriguing phenomenon in fundamental physics: the Kondo effect. The findings are reported in an article published online today in the scientific journal Nature Physics.
The Kondo effect, one of the few examples in physics where many particles collectively behave as one object (a single quantum-mechanical body), has intrigued scientists around the world for decades. When a single magnetic atom is located inside a metal, the free electrons of the metal ‘screen’ the atom. That way, a cloud of many electrons around the atom becomes magnetized. Sometimes, if the metal is cooled down to very low temperatures, the atomic spin enters a so-called ‘quantum superposition’ state. In this state its north-pole points in two opposite directions at the same time. As a result, the entire electron cloud around the spin will also be simultaneously magnetized in two directions.
Now, using a technique that was developed by the same team in 2007, the researchers have shown that it is possible to predict when the Kondo effect will occur – and to understand why. The key turns out to be in the geometry of a magnetic atom’s immediate surroundings. By carefully studying how this geometry influences the magnetic moment (or “spin”) of the atom, the emergence of the Kondo effect can now be predicted and understood.
Dr. Cyrus Hirjibehedin, a member of the IBM team who is now a Lecturer at UCL (University College London) and a part of the academic staff of the LCN, said: “This result represents a major advance in our understanding of this fundamental physical phenomenon and could have important consequences for future nanoscale magnetic devices.”
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Figure A shows a schematic drawing of a single Co atom bound on top of a Cu atom of the Cu2N (copper nitride) surface. Through the Cu2N layer the Co atom is coupled to the electrons in the bulk copper, which can screen the magnetic orientation of the the localized spin on the atom.
Figure B shows a topographic scanning tunnelling microscope (STM) image (10 nm×10 nm) of four Cu2N islands with single Co atoms. The two diagrams at the sides sketch the adsorption site of the two marked Co atoms (Cu and N atoms are depicted as yellow and green circles, respectively). The STM can then be used to study the interaction of the Co atom with its environment.
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About the London Centre for Nanotechnology:
The London Centre for Nanotechnology is an interdisciplinary joint enterprise between University College London and Imperial College London. In bringing together world-class infrastructure and leading nanotechnology research activities, the Centre aims to attain the critical mass to compete with the best facilities abroad. Research programmes are aligned to three key areas, namely Planet Care, Healthcare and Information Technology and bridge together biomedical, physical and engineering sciences. Website: www.london-nano.com
About UCL (University College London):
Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender, and the first to provide systematic teaching of law, architecture and medicine. In the government's most recent Research Assessment Exercise, 59 UCL departments achieved top ratings of 5* and 5, indicating research quality of international excellence. UCL is in the top ten world universities in the 2007 THES-QS World University Rankings, and the fourth-ranked UK university in the 2007 league table of the top 500 world universities produced by the Shanghai Jiao Tong University. UCL alumni include Marie Stopes, Jonathan Dimbleby, Lord Woolf, Alexander Graham Bell, and members of the band Coldplay. Website: www.ucl.ac.uk
About the IBM Almaden Research Centre:
The IBM Almaden Research Center is one of eight laboratories worldwide that make up IBM Research. Almaden has a rich history of achievement including a legacy of disk drive innovation, the creation of an industry - our researchers invented the relational database, establishing the emerging discipline of service science, in addition to being referred to as "the Kitty Hawk of nanotechnology".
The major areas of research at Almaden are Science & Technology, including fundamental science, nanotechnology, spin physics and photoresists; Computer Science, with work in areas such content management, human-computer interaction, text analytics, services-oriented architectures and most recently healthcare informatics; Service Science Research, focusing on large scale, people-and information-intensive challenges and Storage Systems, from storage and file systems to server software and systems management. Additionally, technology licensing is a key element in our value creation strategy and a source of significant mutual benefits for IBM Research and its external partners. Website: www.almaden.ibm.com.