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Quantum interference effect in electron tunneling through a quantum-dot-ring spin valve.

Ma JM, Zhao J, Zhang KC, Peng YJ, Chi F - Nanoscale Res Lett (2011)

Bottom Line: It is shown that the magnitudes of these quantities are sensitive to the relative angle between the leads' magnetic moments and the quantum interference effect originated from the inter-lead coupling.We pay particular attention on the Coulomb blockade regime and find the relative current magnitudes of different magnetization angles can be reversed by tuning the inter-lead coupling strength, resulting in sign change of the TMR.For large enough inter-lead coupling strength, the current spin polarizations for parallel and antiparallel magnetic configurations will approach to unit and zero, respectively.PACS numbers:

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, Bohai University, Jinzhou 121000, China. chifeng@semi.ac.cn.

ABSTRACT
Spin-dependent transport through a quantum-dot (QD) ring coupled to ferromagnetic leads with noncollinear magnetizations is studied theoretically. Tunneling current, current spin polarization and tunnel magnetoresistance (TMR) as functions of the bias voltage and the direct coupling strength between the two leads are analyzed by the nonequilibrium Green's function technique. It is shown that the magnitudes of these quantities are sensitive to the relative angle between the leads' magnetic moments and the quantum interference effect originated from the inter-lead coupling. We pay particular attention on the Coulomb blockade regime and find the relative current magnitudes of different magnetization angles can be reversed by tuning the inter-lead coupling strength, resulting in sign change of the TMR. For large enough inter-lead coupling strength, the current spin polarizations for parallel and antiparallel magnetic configurations will approach to unit and zero, respectively.PACS numbers:

No MeSH data available.


Total current J, current spin polarization p and TMR each as a function of the bias voltage for different values of φ. tLR = 0 in Figs. (a) to (c) and tLR = 0.01 in Figs. (d) to (f). The other parameters are intradot energy level εd = 0, temperature T = 0.01, and polarization of the leads PL = PR = 0.4.
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Figure 2: Total current J, current spin polarization p and TMR each as a function of the bias voltage for different values of φ. tLR = 0 in Figs. (a) to (c) and tLR = 0.01 in Figs. (d) to (f). The other parameters are intradot energy level εd = 0, temperature T = 0.01, and polarization of the leads PL = PR = 0.4.

Mentions: Bias dependence of electric current J = J↑ + J↓, where Jσ = (JLσ - JRσ)/2 is the symmetrized current for spin-σ, current spin polarization p = (J↑ - J↓)/(J↑ + J↓), and TMR=[J(φ = 0) - J(φ)]/J(φ) are shown in Figure 2 for selected values of the angle φ. In the absence of inter-lead coupling (tLR = 0), the electric current in Figure 2(a) shows typical step configuration due to the Coulomb blockade effect. The current step emerged in the negative bias region occurs when the dot level εd is aligned to the Fermi level of the right lead (μR = 0). Now electrons tunnel from the right lead via the dot to the left lead because μL = eV < εεd = 0. The dot can be occupied by a single electron with either spin-up or spin-down orientation, which prevents double occupation on εd due to the Pauli exclusion principle. Since the other transport channel εd + U is out of the bias window, the current keeps as a constant in the bias regime of eV <εd = 0. In the positive bias regime of εd <eV <εd + U a single electron transport sequentially from the left lead through the dot to the right lead, inducing another current step. The step at higher bias voltage corresponds to the case when εd + U crosses the Fermi level. Now the dot may be doubly occupied, and no step will emerge regardless of the increasing of the bias voltage.


Quantum interference effect in electron tunneling through a quantum-dot-ring spin valve.

Ma JM, Zhao J, Zhang KC, Peng YJ, Chi F - Nanoscale Res Lett (2011)

Total current J, current spin polarization p and TMR each as a function of the bias voltage for different values of φ. tLR = 0 in Figs. (a) to (c) and tLR = 0.01 in Figs. (d) to (f). The other parameters are intradot energy level εd = 0, temperature T = 0.01, and polarization of the leads PL = PR = 0.4.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211328&req=5

Figure 2: Total current J, current spin polarization p and TMR each as a function of the bias voltage for different values of φ. tLR = 0 in Figs. (a) to (c) and tLR = 0.01 in Figs. (d) to (f). The other parameters are intradot energy level εd = 0, temperature T = 0.01, and polarization of the leads PL = PR = 0.4.
Mentions: Bias dependence of electric current J = J↑ + J↓, where Jσ = (JLσ - JRσ)/2 is the symmetrized current for spin-σ, current spin polarization p = (J↑ - J↓)/(J↑ + J↓), and TMR=[J(φ = 0) - J(φ)]/J(φ) are shown in Figure 2 for selected values of the angle φ. In the absence of inter-lead coupling (tLR = 0), the electric current in Figure 2(a) shows typical step configuration due to the Coulomb blockade effect. The current step emerged in the negative bias region occurs when the dot level εd is aligned to the Fermi level of the right lead (μR = 0). Now electrons tunnel from the right lead via the dot to the left lead because μL = eV < εεd = 0. The dot can be occupied by a single electron with either spin-up or spin-down orientation, which prevents double occupation on εd due to the Pauli exclusion principle. Since the other transport channel εd + U is out of the bias window, the current keeps as a constant in the bias regime of eV <εd = 0. In the positive bias regime of εd <eV <εd + U a single electron transport sequentially from the left lead through the dot to the right lead, inducing another current step. The step at higher bias voltage corresponds to the case when εd + U crosses the Fermi level. Now the dot may be doubly occupied, and no step will emerge regardless of the increasing of the bias voltage.

Bottom Line: It is shown that the magnitudes of these quantities are sensitive to the relative angle between the leads' magnetic moments and the quantum interference effect originated from the inter-lead coupling.We pay particular attention on the Coulomb blockade regime and find the relative current magnitudes of different magnetization angles can be reversed by tuning the inter-lead coupling strength, resulting in sign change of the TMR.For large enough inter-lead coupling strength, the current spin polarizations for parallel and antiparallel magnetic configurations will approach to unit and zero, respectively.PACS numbers:

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, Bohai University, Jinzhou 121000, China. chifeng@semi.ac.cn.

ABSTRACT
Spin-dependent transport through a quantum-dot (QD) ring coupled to ferromagnetic leads with noncollinear magnetizations is studied theoretically. Tunneling current, current spin polarization and tunnel magnetoresistance (TMR) as functions of the bias voltage and the direct coupling strength between the two leads are analyzed by the nonequilibrium Green's function technique. It is shown that the magnitudes of these quantities are sensitive to the relative angle between the leads' magnetic moments and the quantum interference effect originated from the inter-lead coupling. We pay particular attention on the Coulomb blockade regime and find the relative current magnitudes of different magnetization angles can be reversed by tuning the inter-lead coupling strength, resulting in sign change of the TMR. For large enough inter-lead coupling strength, the current spin polarizations for parallel and antiparallel magnetic configurations will approach to unit and zero, respectively.PACS numbers:

No MeSH data available.