An array of quantum dots as a spin filter device by using Dicke and Fano effects

Abstract

Recently, there has been much interest in understanding the manner in which the unique properties of nanostructures may be exploited in spintronics devices, which utilize the spin degree of freedom of the electron as the basis of their operation [1][2]. A natural feature of these devices is the direct connection between their conductance and their quantum-mechanical transmission properties, which may allow their use as an all-electrical means for generating and detecting spin polarized distributions of carriers.Quantum dots are man-made nanostructures in which electrons are confined in all space dimensions [3]. Energy and charge quantization results from this confinement. As both features are present in real atomic systems, useful analogies between real and artificial atomic systems have been exploited recently. Enforcing this analogy, Fano [4][5] and Dicke effects [6] were also found to be present in quantum dot configurations. On the other hand, Song et al. [2] described how a spin filter may be achieved in open quantum dot systems, by exploiting the Fano resonances that occur in their transmission characteristic. In a quantum dot in which the spin degeneracy of carrier is lifted they showed that the Fano effect may be used as an effective means to generate spin polarization of transmitted carriers and that electrical detection of the resulting polarization should be possible.In a previous work [7], we showed that in side-coupled double quantum-dot system the transmission shows a large peak-to-valley ratio. Moreover, the difference of energy between the resonances and antiresonances can be controlled adjusting the difference between the energy levels of the two quantum dots by gate voltages due to the Dicke effect. The Dicke effect in optics takes place in the spontaneous emission of a pair of atoms radiating a photon with a wavelength much larger than the separation between them [6]. The luminescence spectrum is characterized by a narrow and a broad peak, associated with long and short-lived states, respectively. The former state, coupled weakly to the electromagnetic field, is called subradiant, and the latter, strongly coupled, a superradiant state. In the present work, we show that the above properties can be used to design an efficient spin filter with a quantum dot array system. We show that by controlling the Fano and Dicke effects this system can be used as an efficient spin filter even for small values of the magnetic field.In this work we propose a new design of a spin-dependent polarizer. The device consists of a quantum dot array coupled to leads, as shown schematically in Fig1. By lifting the spin degeneracy of the carriers in a quantum dot by means of a magnetic field, Fano and Dicke effects are used as effective means to generate spin polarization of the electrical current. A detailed analysis of the spin-dependent transmission and polarized current is carried out. For instance, in Fig. 2 we show a contour plot with the weighted spin polarization for a fixed magnetic field of as a function of th...

Coherent two-dimensional spectroscopy of a Fano model

“…The first Fano profiles were observed more than 80 years ago in atomic spectra, including photoionization of atoms and photodissociation of small molecules [3,4]. The field of study was established around scattering processes where the phenomena of coupling to a thermal bath resulting in dissipation or decoherence is not important, except in a few cases, notably pressure broadening [11][12][13].The synthesis and control of matter at the nanoscale opened up the observation of Fano profiles to dissipative systems [14][15][16][17][18] which in turn spurred a renewed interest in theoretical descriptions that would solve the problem in open quantum systems [8][9][10][19][20][21], and correctly account for the relaxation. Consequent with this desire to measure dissipation, more sophisticated spectroscopies are to be invoked.…”

Aharonov–Bohm ring with a side-coupled quantum dot array as a spin switch

“…Recently, motivated by the pioneering work of Datta and Das, 1 there have been a great deal of theoretical and experimental work concerning the possibility of controlling the electron spin by means of the Rashba spin-orbit interaction ͑RSOI͒ with or without the help of the magnetic field and the magnetic material. 6 Recently, Ojeda et al 14 have proposed a spin filter device based on a QD array coupled to leads by using Dicke and Fano effects. [7][8][9] Due to the progress in the nanofabrication of quantum devices, it is possible to fabricate long-range ordered QDs arrays.…”

Coulomb interactions-induced perfect spin-filtering effect in a quadruple quantum-dot cell

“…As a result, the Zeeman splitting of spin-dependent conductances in the region of such an asymmetric peak leads to the emergence of so-called spin-polarized window (SPW) when there is high probability of tunneling for the electrons with spin σ and close-to-zero one for the electrons with spin σ [14][15][16][17] . For the QD-networks previously proposed as spin-filter prototypes in [15][16][17] it is highly preferable to have many QDs considering the Coulomb correlations inside each QD but not between them. In this article we will show that the nanosized diamond-shaped cell composed of just four QDs, a quadruple quantum-dot cell (QQD cell), can display perfect spin filtering properties.…”