Quantum dot as a spin-current diode: A master-equation approach

Souza, F. M.; Egues, J. Carlos; Jauho, Antti–Pekka

doi:10.1103/physrevb.75.165303

Cited by 102 publications

(107 citation statements)

References 50 publications

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“…The tunneling current is usually larger in the parallel configuration, when transport occurs between the majority-majority and minority-minority spin bands, than in the antiparallel configuration, where electrons tunnel between majority and minority spin bands, which gives rise to positive TMR effect. The TMR has been analyzed in various systems, including single-electron transistors and quantum dots [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. In fact, a great deal of theoretical and experimental investigations has been devoted to spin-polarized transport through quantum dot structures.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, such systems are also being considered for applications in future spintronic devices as well as for quantum computing [21]. However, most of existing theoretical considerations of spin-dependent transport in quantum dots involved only single and double dot systems [3,4,5,6,7,8,9,10,11,12,13,14,15,16], while experiments were carried out mainly for single dot structures [22,23,24,25,26,27,28,29,30,31]. In particular, it has been shown [7] that the TMR in quantum dots weakly coupled to ferromagnetic leads is generally smaller than the value given by the Julliere model [1], TMR Jull = 2p 2 /(1 − p 2 ), where p is the spin polarization of the leads, which is characteristic of tunneling through a single tunnel junction.…”

Section: Introductionmentioning

confidence: 99%

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The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads

Weymann

2009

J. Phys.: Condens. Matter

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Abstract. We analyze numerically the spin-dependent transport through coherent chains of three coupled quantum dots weakly connected to external magnetic leads. In particular, using the diagrammatic technique on the Keldysh contour, we calculate the conductance, shot noise and tunnel magnetoresistance (TMR) in the sequential and cotunneling regimes. We show that transport characteristics greatly depend on the strength of the interdot Coulomb correlations, which determines the spacial distribution of electron wave function in the chain. When the correlations are relatively strong, depending on the transport regime, we find both negative TMR as well as TMR enhanced above the Julliere value, accompanied with negative differential conductance (NDC) and super-Poissonian shot noise. This nontrivial behavior of tunnel magnetoresistance is associated with selection rules that govern tunneling processes and various high-spin states of the chain that are relevant for transport. For weak interdot correlations, on the other hand, the TMR is always positive and not larger than the Julliere TMR, although super-Poissonian shot noise and NDC can still be observed.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads

Weymann

2009

J. Phys.: Condens. Matter

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“…The tunneling rates for the majority and minority spins are different (Γ FM ↑ ≠Γ FM ↓ ) for this junction, meaning that there are fewer available states for the minority spins in the ferromagnetic electrode. As a result, the minority spins will spend more time on the dot, leading to spin accumulation [15]. This leads to a decreased current due to electrons with minority spins, resulting in a decreased total conductance through the device for positive bias.…”

mentioning

confidence: 99%

“…We start with an expression for the current [15] derived by employing the master equation approach [29] in the sequential tunneling regime. Using the tunneling rates defined above, we find the total current through a quantum dot with a single ferromagnetic lead to be for the case of positive and negative bias, respectively.…”

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confidence: 99%

Electrically Tunable Spin Polarization in a Carbon Nanotube Spin Diode

Merchant

Marković

2008

Phys. Rev. Lett.

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We have studied the current through a carbon nanotube quantum dot with one ferromagnetic and one normal-metal lead. For the values of gate voltage at which the normal lead is resonant with the single available non-degenerate energy level on the dot, we observe a pronounced decrease in the current for one bias direction.We show that this rectification is spin-dependent, and that it stems from the interplay between the spin accumulation and the Coulomb blockade on the quantum dot. Our results imply that the current is spin-polarized for one direction of the bias, and that the degree of spin polarization is fully and precisely tunable using the gate and bias voltages. As the operation of this spin diode does not require high magnetic fields or optics, it could be used as a building block for electrically controlled spintronic devices.The ability to create, manipulate and detect spin currents is central to the development of spintronic devices [1]. Controlling the spin currents by purely electrical means [2,3] is particularly interesting, as that would allow the integration of spintronic

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“…[14][15][16] A wealth of spin-dependent effects has been observed in this system due to the interplay of quantum confinement, Coulomb correlations, Pauli principle, and leadpolarization alignments. For instance, effects such as spin accumulation, 17,18 spin diode, 19,20 spin blockade, [21][22][23][24] spin current ringing, 25,26 negative differential conductance, and negative TMR 17,21 arise in this context. In order to obtain additional information, not contained in the average current, shot noise has also been analyzed in several spintronic systems.…”

Section: Introductionmentioning

confidence: 99%

Spin-polarized current and shot noise in the presence of spin flip in a quantum dot via nonequilibrium Green’s functions

2008

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Using non-equilibrium Green functions we calculate the spin-polarized current and shot noise in a ferromagnet-quantum-dot-ferromagnet (FM-QD-FM) system. Both parallel (P) and antiparallel (AP) magnetic configurations are considered. Coulomb interaction and coherent spin-flip (similar to a transverse magnetic field) are taken into account within the dot. We find that the interplay between Coulomb interaction and spin accumulation in the dot can result in a bias-dependent current polarization ℘. In particular, ℘ can be suppressed in the P alignment and enhanced in the AP case depending on the bias voltage. The coherent spin-flip can also result in a switch of the current polarization from the emitter to the collector lead. Interestingly, for a particular set of parameters it is possible to have a polarized current in the collector and an unpolarized current in the emitter lead. We also found a suppression of the Fano factor to values well below 0.5.

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Quantum dot as a spin-current diode: A master-equation approach

Cited by 102 publications

References 50 publications

The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads

The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads

Electrically Tunable Spin Polarization in a Carbon Nanotube Spin Diode

Spin-polarized current and shot noise in the presence of spin flip in a quantum dot via nonequilibrium Green’s functions

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