We study an electron transport through a quantum dot in the presence of time-dependent fields. The dot is described by a single level and the intra-dot Coulomb interaction is introduced within the Hartree-Fock approximation. The external fields cause a time-dependent shift of the energy spectrum of the leads and quantum dot. We take into account the spin-polarized solutions for the quantum dot charge. We calculated the time dependence of the current and charge accumulated on the dot, the average current and charge vs. the source-drain and gate voltages in dependence on the Coulomb interaction strength and the frequencies and amplitude of the external fields.
Optical transitions between bound and continuum states in multiple-heterojunction quantum structures are numerically investigated. In the conduction band energy range the absorption to continuum is studied within one-band effective-mass approximation. By changing the shape of quantum wells, we can tune the energy corresponding to absorption peak. We also show how the absorption is modified in the case of annealed structures. The inter-subband transitions in the energy range of valence band in Si/Si_{1-x}Ge_{x}/Si quantum well are described with the help of multiband Luttinger-Kohn Hamiltonian. Particular attention is paid to transitions to resonant states.
Influence of magnetic field on the energy positions and widths of one electron resonance states in a multi-shell spherical quantum dot is investigated. The one-band effective mass approximation is assumed. The complexeigenvalue Schrodinger equation approach involving complex rotation of coordinates is used to obtain complex eigenenergies, E_{r} - iΓ/2, corresponding to resonance states. We show how the magnetic field changes the resonance energy, E_{r}, and decay rate, Γ, yielding bound states for some particular cases.
Magnetic multilayers with a new type of structural modification were prepared by ultrahigh vacuum deposition onto substrates with V-shaped microgrooves and used as the samples for the following two novel studies: One is the study of giant magnetoresistance in a new geometry, CAP, where the electric current is at a certain angle to interfaces. Enhancement of magnetoresistance in CAP geometry, in comparison to the normal current in-plane magnetoresistance, was confirmed. The other is the study of magnetic thin wires, which were prepared by depositing in a tilted direction to the surface. A preliminary result of magnetization reversal investigation is presented.
We use the eight-band k·p model to describe the infrared inter-subband absorption in Si-Si_{1-x}Ge_{x}-Si quantum wells, which takes explicitly into account the Γ'_{25}(Γ_{8}^{+}+Γ_{7}^{+} in the double group) valence band and the second conduction band Γ'_{2}(Γ_{7}ˉ). We then obtain an accurate description of mixing of the S wave function with the valence band functions.
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