Spin-fluctuation-induced dephasing in a mesoscopic ring

We investigate the persistent current in a hybrid Aharonov-Bohm ring–quantum-dot system coupled to a reservoir which provides spin fluctuations. It is shown that the spin exchange interaction between the quantum dot and the reservoir induces dephasing in the absence of direct charge transfer. We demonstrate an anomalous nature of this spin-fluctuation-induced dephasing which tends to enhance the persistent current. We explain our result in terms of the separation of the spin and the charge degrees of freedom. The nature of the spin-fluctuation-induced dephasing is analyzed in detail.