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-Boh m/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 cha nnel plus free electrons in the odd-parity channel. The twisted boundary co nditions representing the fluxes couple slates of opposite parity unless th e twist angles satisfy phi(alpha) = f(alpha)pi, where f(alpha) are integers , with spin index alpha =up arrow,down arrow. For these special values of p hi(alpha), 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 phi(up arrow) = phi(down arrow) is insensitive to the presence of the magnetic impurity/quantum dot.