We find the exact quasiparticle spectrum, elastic S matrix, and free energy for the continuum Kondo problem of k species of electrons coupled to an impurity of spin S. Here, the impurity becomes an immobile quasiparticle sitting on the boundary. The particles are ‘‘kinks,’’ which can be thought of as field configurations interpolating between adjacent wells of a potential with k+1 degenerate minima. For the overscreened case k>2S, the impurity in the continuum is a kink as well, which explains the noninteger number of boundary states.

• Received 3 May 1993

DOI:https://doi.org/10.1103/PhysRevLett.71.2485