Kondo Impurity in a Mesoscopic Ring: Charge Persistent Current

We study the influence of a magnetic impurity or ultrasmall quantum dot on the charge persistent current of a mesoscopic ring. The system consists of electrons in a one-dimensional ring threaded by spin-dependent Aharonov-Bohm/Casher fluxes, coupled via an antiferromagnetic exchange interaction to a localized electron. By passing to a basis of electron states with definite parities, the problem is mapped onto a Kondo model for the even-parity channel plus free electrons in the odd-parity channel. The twisted boundary conditions representing the fluxes couple states of opposite parity unless the twist angles satisfy φ_α = f_απ, where fα are integers, with spin index α = ↑, ↓. For these special values of φ_α, the model is solved exactly by a Bethe ansatz. Special cases are investigated in detail. In particular we show that the charge stiffness in the case φ_↑ = φ_↓ is insensitive to the presence of the magnetic impurity/quantum dot.