We study the linear and nonlinear optical response of intersubband transitions in a semiconductor quantum well. We describe the coupling of the quantum well structure with the electromagnetic field by using the nonlinear density matrix equations, in the two-subband approximation. We provide proper approximate analytical solutions to these equations that are used for the closed-form determination of the optical susceptibilities χ(1)">χ(1), χ(3)">χ(3), and χ(5)">χ(5). We also explore the dependence of χ(1)">χ(1), χ(3)">χ(3), and χ(5)">χ(5) on the electron sheet density for a specific double GaAs/AlGaAs quantum well.

Under the influence of different external stimuli condensed matter reveals its magnificent properties. The electric field, the temperature, the concentration gradients and the light are the basic “forces” responsible for processes such as the electrical, the thermal, the diffusion transport or optical phenomena. The action of the magnetic field brings about the galvanomagnetic or the thermomagnetic effects. New alloy semiconductors and the development of artificial semiconductor heterostructures led to the confinement of carriers in two, one or zero dimensions, opening a new window in condensed matter research. The application of a perpendicular magnetic field upon two-dimensional carriers, led to the discovering of astonishing phenomena, namely, the integer or the fractional quantum Hall effects and inspired radical theoretical interpretations. The reduced symmetry of low dimensional structures enhances decisively the role of the magnetic field orientation, bringing to light novel and unexpected phenomena. In the present book the effect of the application of an in-plane magnetic field upon low dimensional carriers, giving rise to impressive novel phenomena, is presented and discussed. Specifically, whenever a quantum well is subjected to an in-plane or tilted magnetic field, the elegant concept of Landau levels must be modified, because the carriers move under the competing influence of the Lorentz force and the force due to the quantum well confining potential. Under these conditions, the equal-energy surfaces or equivalently, the density of states (DOS), are qualitatively and quantitatively modified. The DOS diverges significantly from the ideal step-like two-dimensional carrier form. The book discusses various physical properties which are affected by the DOS modification.

We have developed a quantum-mechanical theory for the interaction of light and electron-hole excitations in semiconductor quantum dots. Our theoretical analysis results in an expression for the photoluminescence intensity in the non-linear regime. The validity of the theoretical results is tested analyzing experimental data reported for the temperature dependence of the emission spectra of an individual lens-shaped In0.4Ga0.6As self-assembled quantum dot in a wide temperature range up to 300 K. Our theoretical predictions for the redshift of the emission peak with increasing temperature, in the range 2–300 K, agree with the experiment.

We systematically examine all the tight-binding parameters pertinent to charge transfer along DNA. The pi molecular structure of the four DNA bases (adenine, thymine, cytosine, and guanine) is investigated by using the linear combination of atomic orbitals method with a recently introduced parametrization. The HOMO and LUMO wave functions and energies of DNA bases are discussed and then used for calculating the corresponding wave functions of the two B-DNA base-pairs (adenine-thymine and guanine-cytosine). The obtained HOMO and LUMO energies of the bases are in good agreement with available experimental values. Our results are then used for estimating the complete set of charge transfer parameters between neighboring bases and also between successive base-pairs, considering all possible combinations between them, for both electrons and holes. The calculated microscopic quantities can be used in mesoscopic theoretical models of electron or hole transfer along the DNA double helix, as they provide the necessary parameters for a tight-binding phenomenological description based on the pi molecular overlap. We find that usually the hopping parameters for holes are higher in magnitude compared to the ones for electrons. Our findings are also compared with existing calculations from first principles.

We study the interaction of chirped electromagnetic pulses with intersubband transitions of a double semiconductor quantum well. We consider the ground and first excited subbands and give emphasis to controlled intersubband population transfer. The system dynamics is described by the nonlinear density matrix equations that include the effects of electron-electron interactions. These equations are solved numerically for various values of the electron sheet density for a realistic double GaAs/AlGaAs quantum well, and the efficiency of population transfer is discussed.

We study the interaction of a chirped electromagnetic pulse with intersubband transitions of a double semiconductor quantum well. We specifically consider the interaction of the ground and first excited subbands with the electromagnetic field and use the nonlinear density matrix equations for the description of the system dynamics. These equations are solved numerically for various values of the electron sheet density for a realistic double GaAs/AlGaAs quantum well, and the efficiency of population transfer is discussed with emphasis given to the effects of the detuning of the central frequency of the electromagnetic field from resonance.

In order to explain the absence of hysteresis in ferromagnetic p-type (Cd,Mn)Te quantum wells (QWs), spin dynamics was previously investigated by Monte Carlo simulations combining the Metropolis algorithm with the determination of hole eigenfunctions at each Monte Carlo sweep. Short-range antiferromagnetic superexchange interactions between Mn spins—which compete with the hole-mediated long-range ferromagnetic coupling—were found to accelerate magnetization dynamics if the layer containing Mn spins is wider than the vertical range of the hole wave function. Employing this approach it is shown here that appreciate magnitudes of remanence and coercivity can be obtained if Mn ions are introduced to the quantum well in a delta-like fashion.