Theoretical Investigation of Nonequilibrium Spin Transport Through a Triple Site Quantum Wire System
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ORIGINAL PAPER
Theoretical Investigation of Nonequilibrium Spin Transport Through a Triple Site Quantum Wire System Yangdong Zheng 1,2 Received: 11 February 2020 / Accepted: 10 July 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
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. Keywords Quantum wire system . Nonequilibrium spin transport . Keldysh formalism . Hartree-Fock approximation PACS numbers 73.21.Hb . 72.10.-d . 73.23.-b . 73.63.Rt
1 Introduction Spintronics, which exploits quantum spin states of electrons to realize some special electronic feature and deal with possible application, is a relative novel field and has shown excellent characteristics in present research and will play an important role in future electronics [1,2]. Particularly, since lowdimensional semiconductor systems (quantum wells, wires, and dots) have their great flexibility in manipulating the quantum state of electrons, the quantum spin properties in such systems become the important subject in recent spintronics research. The representative spintronic phenomenon is the * Yangdong Zheng [email protected] 1
Research and Development Department, Mitsubishi Electric (China) Company Limited, Shanghai 200336, China
2
Research Center for Low Temperature and Materials Sciences, Kyoto University, Kyoto 606-8501, Japan
giant magnetoresistance (GMR) observed in thin film structures composed of alternating ferromagnetic and nonmagnetic metal layers, which shows a significant difference in electrical resistance when the direction of magnetization of adjacent ferromagnetic layers is parallel or anti-parallel. The resistance is normally higher in the anti-parallel
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