H.A. Sarkisyan

Nonlinear optical properties in a nanoring: quantum size and magnetic field effect.

We have studied the nonlinear optical absorption and the nonlinear optical rectification of an exciton in a nanoring in the presence of magnetic flux. The calculation results show that one can control the properties of nonlinear optical absorption and nonlinear optical rectification of a nanoring by tuning the outer and inner radius. Moreover, we find that the nonlinear optical properties of a nanoring can be modulated by the magnetic flux through the nanoring.

Impurity states in a narrow band gap semiconductor quantum dot with parabolic confinement potential

Abstract Impurity states in a narrow band gap semiconductor quantum dot are studied theoretically. The quantum dot confinement potential is approximated by the three-dimensional spherically symmetric parabolic potential. The electron dispersion law is considered within the framework of two-band Kane model. It is shown that the nonparabolicity leads to the Schroedinger equation with the effective oscillatory potential containing terms proportional to 1/ r , r, r 4 . Within the framework of the stationary theory of perturbation the energy corrections due to these terms are calculated.

Interband transitions in a spherical quantum layer in the presence of an electric field: Spherical rotator model

The interband transitions in a spherical GaAs quantum layer in the presence of an arbitrarily directed electric field are studied theoretically within the framework of the rigid spherical rotator model. The problem is solved under the assumption that the external field is a perturbation. Within the framework of the dipole approximation an expression for the interband absorption coefficient is obtained, and the absorption threshold frequency is determined. The corresponding selection rules are derived. A comparison with the case of quantum transitions in a spherical quantum layer in the presence of a radial electric field is performed.

Two electronic states in spherical quantum nanolayer

In this paper two electronic states in spherical quantum nanolayer are discussed. The Coulomb interaction between the electrons is discussed as perturbation. For confinement potential of the nanolayer the three-dimensional radial analog of Smorodinsky-Winternitz potential is considered. The problem is discussed within the frameworks of Russell-Saunders coupling scheme, thus, the spin-orbit interaction is considered weak. Therefore the eigenfunctions of the system is represented as a multiplication of its coordinate wave function and spin wave function. For this system the analogue of helium atom theory is represented. The eigenfunctions and energy states are obtained for one and two electron cases in the spherical quantum nanolayer. For the spherical nanolayer the dependence of perturbation energy, unperturbed system energy and the total energy for the ground state upon the inner radius is represented when the outer radius is fixed.

On the possibility of implementation of Kohn’s theorem in the case of ellipsoidal quantum dots

An electron gas in a strongly oblated ellipsoidal quantum dot with impenetrable walls is considered. Influence of the walls of the quantum dot is assumed to be so strong in the direction of the minor axis (the OZ axis) that the Coulomb interaction between electrons in this direction can be neglected and considered as two-dimensional, coupled. On the basis of geometric adiabaticity we show that in the case of a few-particle gas a powerful repulsive potential of the quantum dot walls has a parabolic form and localizes the dot in the geometric center of the structure. Due to this fact, conditions occur to implement the generalized Kohn theorem for this system.

Optical absorption in GaAs quantum wells caused by donor–acceptor pair transitions

Optical absorption related to donor–acceptor pair transitions in GaAs quantum wells was theoretically investigated. The donor and acceptor ground state wavefunctions and energies were obtained using variational method in the frames of the effective mass approximation. The absorption coefficient related to acceptor-to-donor transition was calculated. The spreading of the absorption curve as a result of averaging over impurity distances was taken into account. The character of the dependence of the absorption coefficient on both quantum well thickness and impurity concentration was determined. The blueshift in the absorption spectra was theoretically investigated. Comparison with available experimental data was made.

Energy levels of an electron with Kane's law of dispersion in a spherical microcrystal

Abstract The electronic states in a spherical semiconductor microcrystal are studied theoretically taking into account the nonparabolicity of electron dispersion law. The microcrystal confinement potential is approximated by the three-dimensional spherically symmetric parabolic potential. It is shown that the nonparabolicity leads to the Schroedinger equation with the effective oscillatory potential containing an “anharmonic” term proportional to r4. Within the framework of the stationary theory of perturbation the energy corrections due to the “anharmonicity” are calculated. The problem of partial removal of electronic energy level degeneracy is discussed.

Magnetoexcitonic states in a quantum ring with the Winternitz-Smorodinsky confinement potential

We investigate magnetoexcitonic states in the Ga1−x1Alx1As/GaAs/Ga1−x2Alx2 As quantum ring with the Winternitz-Smorodinsky confinement potential. A homogeneous magnetic field is directed perpendicularly to the ring plane. The Coulomb interaction between the electron and hole is assumed as weak and is considered in the framework of perturbation theory. Obtained results show that the more realistic Winternitz-Smorodinsky confinement potential, which takes into account a peculiar smoothing of the confinement potential profile, leads to raising of the electron energy levels as compared to the case of a finite-height rectangular confinement potential.

Optical absorption in a narrow-band InSb cylindrical layered nanowire in the presence of strong electrostatic field

On the example of InSb we consider the influence of a strong homogeneous electrostatic field on the state of carriers in a narrow-band quantized cylindrical layer in the case of Kaine dispersion law. Explicit expressions for the energy spectrum and wave function envelopes of charge carriers in the heterolayer are obtained. It is shown that under action of the strong external field the rotational motion, with respect to angular variables, of charge carriers becomes oscillatory in a narrow cone of the azimuth angle. We have obtained corresponding selection rules and calculated the threshold frequencies of absorption for interband and intraband electro-optical transitions in the layer. The threshold frequencies are determined by the geometric sizes of the sample and the magnitude of the external field.

Adiabatic Approach to the Problem of a Quantum Well with a Hydrogen-Like Impurity *

An adiabatic method is presented for solving a boundary discrete spectrum problem for a parabolic quantum well and a rectangular quantum well with infinitely-high walls in the presence of a hydrogen-like impurity. The upper and lower bounds for the energy of the ground state of the systems are obtained under the conditions of the shift of the Coulomb center in a given range of the parameter with respect to earlier variational estimates. The comparison of the rate of convergence of the adiabatic expansion of the solution in parametric bases in the cylindrical and spherical coordinates is carried out.