Quantum Transport Through Semiconductor Quantum-well Structure And One-dimensional Optical Lattice System

In this thesis the quantum transport through semiconductor heterostructures quantum-well structure and one-dimensional optical lattice system are investigated by means of the scattering matrix and transfer-matrix techniques. Our arm is to explore the physical mechanisms of the effects, and to supply physical models and make theoretical validity in designing novel quantum filtering devices with better properties.First, using the effective-mass approximation and Floquet theory, we study the electron transmission over a quantum well in semiconductor heterostructures with Dresselhaus spin-orbit coupling and an applied oscillation field. It is demonstrated by the numerical evaluations that Dresselhaus spin-orbit coupling eliminates the spin degeneracy and leads to the splitting of asymmetric Fano-type resonance peaks in the conductivity. In turn, the splitting of Fano-type resonance induces the spin-polarization-dependent electron current. The location and line shape of Fano-type resonance can be controlled by adjusting the oscillation frequency and the amplitude of the external field as well. These interesting features may be a very useful basis for devising tunable spin filters.Secondly, we have investigated theoretically the field-driven electron transport through a double-quantum-well semiconductor-heterostructure with spin-orbit coupling. The numerical results demonstrate that the transmission spectrums are divided into two sets due to the bound-state level-splitting and each set contains two asymmetric resonance peaks which may be selectively suppressed by altering the phase difference between two driving fields. When the phase difference changes from 0 toπ, the dip of asymmetry resonances shifts from one side of resonance peaks to the other and the asymmetric Fano resonances degenerate into the symmetric Breit-Wigner resonance at a critical value of phase difference. Within a given energy range of incident electron, the spin polarization of transmission current is completely governed by the phase difference which may be used to realize the tunable spin filtering.Then, as is well known to all, the more practical oscillation-type is dipole-oscillation in most of experimental setup, and the dipole-type is easier to exploit experimentally than the spatially uniform field. We study the spin-dependent electron transmission through a quantum well driven by both dipole-type and homogeneous oscillating fields. The numerical evaluations show the dipole modulation and the homogeneous modulation are equivalent. Therefore using the splitting of asymmetric Fano-type resonance peaks in the conductivity, we predict that the dipole-type oscillation, which is more practical in the experimental setup, can be used to realize the tunable spin filters by adjusting the field oscillation-frequency and the amplitude as well.Finally, we study the transport of atoms across a localized Bose-Einstein condensate in an one-dimensional optical lattice with a single defect. The defect potential and the nonlinear parameter of local BEC can be controlled by laser and magnetic fields, thus we can regulate the size of Fano resonance peaks and the location of block point (the position of total reflection) by changing them. Our analytical and numerical results show that the transmission beam of atoms can control by tuning them. These interesting features may be a very useful theoretical basis for devising tunable atom filters.