Thermodynamics of a magnetic impurity in a small metallic grain

We consider a small metallic sphere with a spin-1/2 impurity at its center. For a contact Kondo exchange and equally spaced s states, the problem is reduced to the Bethe Ansatz solution of the Kondo model in a finite box. The energy spacing is an additional energy scale competing with the Kondo temperature. We obtain the energy levels as a function of T-K for four s states. The entropy and the susceptibility are exponentially activated at low T. The low-T results depend on the purity of the number of s-states. (C) 2003 American Institute of Physics.