Theoretical Investigation of Nonequilibrium Spin Transport Through a Triple Site Quantum Wire System

Abstract

A triple lattice site quantum wire (QW) system is chosen to investigate nonequilibrium spin transport properties theoretically. We calculate the initial charge of the QW from the exactly derived ground state. Based on the Keldysh formalism, we describe theoretical methods and derive analytical formulas for nonequilibrium spin transport of the QW systems within Hartree-Fock approximation when Coulomb interactions are present. We report the numerical results of the nonequilibrium differential spin conductance, spin transport current, and electronic charge distribution of the triple site QW system. When only including Coulomb repulsions between the spin-up and spin-down electrons, the series of peaks and valleys in the conductance characteristics appears due to the spin resonant tunneling and spin blockade. With the increase of Coulomb interaction energy U, the conductance peaks start to split into two corresponding to the spin-up and spin-down conductance. Near the resonant points, the spin current polarization and the in-site spin charge polarizations take place. When additionally including spin-spin interactions, the differences between the spin-up and spin-down conductance characteristics are reduced, implying that the spin split is relaxed by spin-spin interactions. The spin splits, the spin current, and spin charge polarizations are relaxed at high temperatures due to the thermal fluctuations.