Inelastic Cotunneling Current and Shot Noise of an InteractingQuantum Dot with Ferromagnetic Correlations

We explore inelastic cotunneling through a strongly Coulomb-blockadedquantum dot attached to two ferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach. We first develop a Bloch-type equation microscopically to describe thecotunneling-induced spin relaxation dynamics, and then develop explicitanalytical expressions for the local magnetization, current, and itsfluctuations. On this basis, we predict a novel zero-bias anomaly ofthe differential conductance in the absence of a magnetic field for theanti-parallel configuration, and asymmetric peak splitting in a magnetic field. Also, for the same system with large polarization, we find a negativezero-frequency differential shot noise in the low positive bias-voltageregion. All these effects are ascribed to rapid spin-reversal due tounderlying spin-flip cotunneling.