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.

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.