Phonon-assisted spin-polarized tunneling through an interacting quantum dot

Abstract

Using the nonequilibrium Green function technique we study theoretically spin-polarizedtransport in double-barrier tunneling junctions based on a single-level quantum dotinteracting with a local phonon mode. Phonon emission and absorption spectra have beencalculated for arbitrary Coulomb correlations on the dot and for different temperatures. Itis shown that in the nonlinear response regime the electron–phonon interaction gives rise tocurrent suppression in symmetric junctions as well as to oscillations of the tunnelmagnetoresistance (TMR). In asymmetric junctions, the same mechanism may leadeffectively to enhancement of the diode-like characteristics. We have also found that atsufficiently low temperatures additional phonon-induced resonance peaks appear in thelinear spectral function on both sides of the main resonance peaks corresponding to thequantum dot energy levels. The case of negative effective charging energy is also analyzednumerically. A significant enhancement of electric current (or suppression of TMR) abovethe threshold bias voltages at which the dot energy level enters the tunneling window isobserved. The gate voltage-controlled rectification effect of the tunneling current inasymmetric junctions with positive and negative effective Coulomb correlations is alsodiscussed.