The Kondo effect and entanglement - Ian Affleck

At low temperatures, a spin-1/2 impurity in a metal forms a spin singlet with a conduction electron delocalized over a length scale which grows exponentially as the Heisenberg coupling of the impurity to the conduction electrons gets weaker. This ubiquitous phenomenon played an important role in the development of renormalization group theory and is believed to occur in systems ranging from quantum dots to heavy fermion materials. I will review the Kondo effect and show how it can be understood in terms of entanglement entropy and resonating valence bonds in spin chains.