Colloquium on June 14, 2010

Ian Affleck
University of Britsh Columbia

The Kondo screening cloud: what it is and how to observe it

Theory suggests that the screening of a magnetic impurity by conduction electrons, the Kondo effect, involves a quantum-entangled state of the impurity spin with the spin of a conduction electron in an orbital with a very large radius of order a micron. Such a large screening cloud has never been observed experimentally and sometimes doubted theoretically. I will review the reasons for this experimental difficulty, possible experiments which might eventually detect it and the insight into this problem provided by the perspective of entanglement entropy.