Switching of Current Spin Polarization by Electron-Phonon Interaction in a Quantum Dot Device

We study spin-polarized electron transport through a quantum dot coupled to one normal metal lead and one ferromagnetic lead. Both the intradot Coulomb correlation and the electron-phonon interaction are taken into account in the framework of nonequilibrium Green's function theory. We find that due to the interplay of the Coulomb blockade effect and the phonon-induced extra electron transport channels, the spin polarization of the electron current driven by external bias voltage is enhanced in a range of negative biases in which the current is flowing from the ferromagnetic lead to the normal metal one. While for the corresponding positive biases, the current polarization is suppressed to negative values where the current is flowing from the normal metal lead to the ferromagnetic one. The device thus operates as a current polarization switcher without the need of a magnetic field or spin-orbit interaction, and may find use in low-power spintronic devices with the help of phonon engineering techniques.