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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.


Tunneling current, current polarization and TMR each as a function of the bias voltage for different values of leads' polarization and fixed φ = π/2. The other parameters are as in Fig. 2.
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Figure 3: Tunneling current, current polarization and TMR each as a function of the bias voltage for different values of leads' polarization and fixed φ = π/2. The other parameters are as in Fig. 2.

Mentions: We now fix tLR = 0.01 and the angle φ = π/2, i.e., the magnetic moments of the leads are perpendicular to each other, to examine the bias dependence of these quantities for different values of leads' polarization PL = PR = P . The electric currents in the bias voltage ranges of eV <εd and eV >εd + U. are monotonously suppressed with the increase of P [Figure 3(a)]. This is because the spin accumulation on the dot in these bias ranges is enlarged by the increase of the leads' spin polarization. In the Coulomb blockade region, however, current magnitudes of different P are identical. The reason is that in this region the spin accumulation induced by the Pauli exclusion principle, which was previously discussed, plays a decisive role compared with that brought about by the leads' spin polarization. As is expected, the current spin polarization is increased with increasing P , which is shown in Figure 3(b). The magnitude of the TMR in Figure 3(c) increases with increasing P. For the half-metallic leads (PL = PR = P = 1), the magnitude of the TMR is much larger than those of usual ferromagnetic leads (Pβ < 1). All these results are similar to those of a single dot case[14-16].


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)

Tunneling current, current polarization and TMR each as a function of the bias voltage for different values of leads' polarization and fixed φ = π/2. The other parameters are as in Fig. 2.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Tunneling current, current polarization and TMR each as a function of the bias voltage for different values of leads' polarization and fixed φ = π/2. The other parameters are as in Fig. 2.
Mentions: We now fix tLR = 0.01 and the angle φ = π/2, i.e., the magnetic moments of the leads are perpendicular to each other, to examine the bias dependence of these quantities for different values of leads' polarization PL = PR = P . The electric currents in the bias voltage ranges of eV <εd and eV >εd + U. are monotonously suppressed with the increase of P [Figure 3(a)]. This is because the spin accumulation on the dot in these bias ranges is enlarged by the increase of the leads' spin polarization. In the Coulomb blockade region, however, current magnitudes of different P are identical. The reason is that in this region the spin accumulation induced by the Pauli exclusion principle, which was previously discussed, plays a decisive role compared with that brought about by the leads' spin polarization. As is expected, the current spin polarization is increased with increasing P , which is shown in Figure 3(b). The magnitude of the TMR in Figure 3(c) increases with increasing P. For the half-metallic leads (PL = PR = P = 1), the magnitude of the TMR is much larger than those of usual ferromagnetic leads (Pβ < 1). All these results are similar to those of a single dot case[14-16].

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.