The spin-dependent electron transport has been studied in magnetic semiconductor waveguides (nanowires) in the helical magnetic field. We have shown that -- apart from the known conductance dip located at the magnetic field equal to the helical-field
amplitude $B_h$ -- the additional conductance dips (with zero conductance) appear at magnetic field different from $B_h$. This effect occuring in the non-adiabatic regime is explained as resulting from the resonant Landau-Zener transitions between the spin-splitted subbands.
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 fie
ld 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.
A spin-dependent quantum transport is investigated in a paramagnetic resonant tunneling diode (RTD) based on a Zn$_{1-x}$Mn$_x$Se/ZnBeSe heterostructure. Using the Wigner-Poisson method and assuming the two-current model we have calculated the curren
t-voltage characteristics, potential energy profiles and electron density distributions for spin-up and spin-down electron current in an external magnetic field. We have found that -- for both the spin-polarized currents -- two types of the current hysteresis appear on the current-voltage characteristics. The current hysteresis of the first type occurs at the bias voltage below the resonant current peak and results from the accumulation of electrons in the quantum well layer. The current hysteresis of the second type appears at the bias voltage above the resonant current peak and is caused by the creation of the quasi-bound state in the left contact region and the resonant tunneling through this quasi-bound state. The physical interpretation of both the types of the current hysteresis is further supported by the analysis of the calculated self-consistent potential profiles and electron density distributions. Based on these results we have shown that -- in certain bias voltage and magnetic field ranges -- the spin polarization of the current exhibits the plateau behavior with the nearly full spin polarization. This property is very promising for possible applications in spintronics.
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 ap
plied 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 $sim$10), the appearance of the linear current versus bias voltage behaviour within the negative-differential resistance region, and the bistability of the current-voltage characteristics. The analysis of the self-consistent potential energy profiles and electron density distribution allowed us to provide a physical interpretation of these properties.
