A spin-and time-dependent electron transport has been studied in a paramagnetic resonant tunneling diode using the self-consistent Wigner-Poisson method. Based on the calculated currentvoltage characteristics in an external magnetic field we have demonstrated that under a constant bias both the spin-up and spin-down current components exhibit the THz oscillations in two different bias voltage regimes. We have shown that the oscillations of the spin-up (down) polarized current result from the coupling between the two resonance states: one localized in the triangular quantum well created in the emitter region and the second localized in the main quantum well. We have also elaborated the one-electron model of the current oscillations, which confirms the results obtained with the Wigner-Poisson method. The spin current oscillations can lower the effectiveness of spin filters based on the paramagnetic resonant tunneling structures and can be used to design the generators of the spin polarized current THz oscillations that can operate under the steady bias and constant magnetic field. a

The theoretical description has been proposed for the operation of the spin transistor in the gate-controlled InAs nanowire. The calculated current-voltage characteristics show that the current flowing from the source (spin injector) to the drain (spin detector) oscillates as a function of the gate voltage, which results from the precession of the electron spin caused by the Rashba spin-orbit interaction in the vicinity of the gate. We have studied two operation modes of the spin transistor: (A) the ideal operation mode with the full spin polarization of electrons in the contacts, the zero temperature, and the single conduction channel corresponding to the lowest-energy subband of the transverse motion and (B) the more realistic operation mode with the partial spin polarization of the electrons in the contacts, the room temperature, and the conduction via many transverse subbands taken into account. For mode (A) the spin-polarized current can be switched on/off by the suitable tuning of the gate voltage, for mode (B) the current also exhibits the pronounced oscillations but with no-zero minimal values. The computational results obtained for mode (B) have been compared with the recent experimental data and a good agreement has been found.

A proposal of a spin separator based on the spin Zeeman effect in Y-shaped nanostructure with a quantum point contact is presented. Our calculations show that the appropriate tuning of the quantum point contact potential and the external magnetic field leads to the spin separation of the current: electrons with opposite spins flow through the different output branches. We demonstrate that this effect is robust against the scattering on impurities. The proposed device can also operate as a spin detector, in which -depending on the electron spin -the current flows through one of the output branches.PACS numbers: 72.25.Dc A design of a controllable source of spin-polarized electrons and an efficient injection of the spin-polarized current into a semiconductor is a basic requirement for a fabrication of novel spintronic devices. The original idea of the spin transistor 1 was assumed that spin-polarized charges are injected into semiconductor channel from the ferromagnetic contact. However, due to the conductivity mismatch between the ferromagnetic and semiconductor materials, the efficiency of the spin injection at ferromagnet/semiconductor interface is rather low -experimentally reported at the level of a few percent. [2][3][4] The low spin-injection rate results in the low signal in the experimental realization of the spin transistor. 5 In order to overcome the conductivity mismatch, the spinpolarized current is injected into the semiconductor using the magnetic semiconductors. 6,7 In the experiments with the magnetic-semiconductor/semiconductor interface, the spin polarization rate reaches the value as high as 90 %. 8-10 Moreover, the use of magnetic semiconductors in resonant tunneling structures allows to construct the spin filter, in which the polarization of the current can be changed from fully spin-down to fully spin-up polarized by the bias voltage. 11,12 In our recent paper, 13 we have studied the spin filter effect in the resonant tunneling diode based on ferromagnetic GaMnN and shown that the spin filter operation can be realized even at room temperature. Several alternative methods to achieve the spin-polarizing effect in semiconductor nanostructures have been recently demonstrated in nanowires with spin-orbit interaction, 14,15 quantum dots, 16 and carbon nanotubes. 17 Although all these devices allow to obtain the spin polarized current, they do not separate the current into the beams with opposite spin. This operation is more complicated and requires the application of the device with at least three terminals: one terminal acts as the input through which the unpolarized current is injected, and the other two terminals act as outputs, through which the spin polarized beams flow out of the device. The spin separation effect in the presence of the spin-orbit interaction has been theoretically predicted in the ballistic T-shaped 18 and Y-shaped 19,20 structures as well as quantum rings. 21 The spin-orbit interaction in-duced by the quantum point contact (QPC) has been recently applied to reproduce the St...

The electron transport through the triple-barrier resonant tunnelling diode (TBRTD) have been studied by the self-consistent numerical method for the Wigner-Poisson problem. The electron flow through the TBRTD can be controlled by the gate voltage applied to one of the potential well regions. For different gate voltage values we have determined the current-voltage characteristics, potential energy profiles, and electron density distribution. We have found the enhancement of the peak-to-valley ratio (up to ∼10), the appearance of the linear current versus bias voltage behaviour within the negative-differential resistance region, and the bistability of the currentvoltage characteristics. The analysis of the self-consistent potential energy profiles and electron density distribution allowed us to provide a physical interpretation of these properties.

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We have investigated the spin current polarization without the external magnetic field in the resonant tunneling diode with the emitter and quantum well layers made from the ferromagnetic GaMnN. For this purpose we have applied the self-consistent Wigner-Poisson method and studied the spin-polarizing effect of the parallel and antiparallel alignment of the magnetization in the ferromagnetic layers. The results of our calculations show that the antiparallel magnetization is much more advantageous for the spin filter operation and leads to the full spin current polarization at low temperatures and 35 % spin polarization of the current at room temperature.The progress in homo-and heteroepitaxy of dilute magnetic semiconductors 1-8 (DMS's) during the past decade allows to fabricate spintronic nanodevices, in which the spin polarization of the current can be controlled by the magnetic or electric field. The spin filter effect in a resonant tunneling diode (RTD) with paramagnetic quantum well embedded in II-VI DMS (ZnMnSe) was studied theoretically 9-11 and experimentally demonstrated by Slobodskyy et al. 12 For the paramagnetic RTD, in the presence of the external magnetic field, the exchange interaction between the conduction band electrons and the Mn 2+ ions leads the giant Zeeman splitting 13 of the quasi-bound state in the paramagnetic quantum-well. This splitting causes that the resonance conditions for the spin up and spin down electrons are satisfied for different bias voltages leading to the separation of the spin current components and consequently to the spin polarization of the current. The spin filter effect in the paramagnetic RTD is limited to very low temperature and requires the high external magnetic field. 12,13 These restrictions cause that more interest is directed towards the application of the ferromagnetic III-V semiconductors, especially those with high Curie temperature, e.g. GaMnAs 8,14-16 or GaMnN. 17,18 Ohno et al. 19 experimentally studied the ferromagnetic RTD based on GaMnAs in which the spin splitting was observed without external magnetic field but it still requires low temperature. Hovewer, the recent experiments reported that GaMnN can exhibit the ferromagnetic properties above room temperature 20-22 at which the exchange splitting of the conduction band is about few tens of meV 23 and remains in the limit of thin layer of a few nanometer width. 24 Although the ferromagnetism in GaMnN is still unresolved theoretical problem, the spin filter effect in the RTD's based on GaMnN is a subject of research carried out by many groups. Recently, Li et al. 25 have theoretically investigated the ferromagnetic RTD consisted of the InGaN quantum well between two GaMnN barriers. In Ref. 25 the spin polarization of the current without magnetic field has been predicted at low temperature but at room temperature it has been reduced to only 8 %. Another way to obtain the spin polarization of the current at room temperature was proposed by Qui el at. 26 who stated that the δ doping of the GaN quant...

We consider the dynamics of interpersonal relations which leads to balanced states in a fully connected network. Here this approach is applied to directed networks with asymmetric relations, and it is generalized to include self-evaluation of actors, according to the ‘looking-glass self’ theory. A new index of self-acceptance is proposed: the relation of an actor to him/herself is positive, if the majority of his/her positive relations to others are reciprocated. Sets of stable configurations of relations are obtained under the dynamics, where the self-evaluation of some actors is negative. Within each set all configurations have the same structure.

The electronic energy levels of one-dimensional aperiodic systems driven by a homogeneous electric field are studied by means of a phase-space description based on the Wigner distribution function. The formulation provides physical insight into the quantum nature of the electronic states for the aperiodic systems generated by the Fibonacci and Thue-Morse sequences. The nonclassical parameter for electronic states is studied as a function of the magnitude of homogeneous electric field to achieve the main result of this work, which is to prove that the nonclassical properties of the electronic states in the aperiodic systems determine the transition probability between electronic states in the region of anticrossings. The localization properties of electronic states and the uncertainty product of momentum and position variables are also calculated as functions of the electric field.