Microscopic theory of the activated behavior of the quantized Hall effect

The thermally activated behavior of the gate defined narrow Hall bars is studied by analyzing the existence of the incompressible strips within a Hartree-type approximation. We perform self-consistent calculations considering the linear response regime, supported by a local conductivity model. We investigate the variation of the activation energy depending on the width of samples in the range of $2d\sim [1-10] \mu m$. We show that the largest activation energy of high-mobility narrow samples, is at the low field edge of Hall filling factor 2 plateau (exceeding half of the cyclotron energy), whereas for relatively wide samples the higher activation energy is obtained at the high field edge of Hall plateau. In contrast to the single-particle theories based on the localization of electronic states, we found that the activation energy is almost independent of the properties of the density of states.Comment: 8 pages, 4 figure

Interaction mediated asymmetries of the quantized Hall effect

Experimental and theoretical investigations on the integer quantized Hall effect in gate defined narrow Hall bars are presented. At low electron mobility the classical (high temperature) Hall resistance line RH(B) cuts through the center of all Hall plateaus. In contrast, for our high mobility samples the intersection point, at even filling factors \nu = 2; 4 ..., is clearly shifted towards larger magnetic fields B. This asymmetry is in good agreement with predictions of the screening theory, i. e. taking Coulomb interaction into account. The observed effect is directly related to the formation of incompressible strips in the Hall bar. The spin-split plateau at \nu= 1 is found to be almost symmetric regardless of the mobility. We explain this within the so-called effective g-model.Comment: 4 pages, 3 figure

Theoretical investigation of InAs/GaSb type-II pin superlattice infrared detector in the mid wavelength infrared range

In this study, we present the theoretical investigation of type-II InAs/GaSb superlattice p-i-n detector. Kronig-Penney and envelope function approximation is used to calculate band gap energy and superlattice minibands. Variational method is also used to calculate exciton binding energies. Our results show that carriers overlap increases at GaSb/InAs interface on the higher energy side while it decreases at InAs/GaSb interface on the lower energy side with increasing reverse bias due to shifting the hole wavefunction toward to the GaSb/InAs interface decisively. Binding energies increase with increasing electric field due to overall overlap of electron and hole wave functions at the both interfaces in contrast with type I superlattices. This predicts that optical absorption is enhanced with increasing electric field. © 2013 American Institute of Physics

Electron transport in electrically biased inverse parabolic double-barrier structure

BATI, Mehmet/0000-0001-7154-2198; BATI, Mehmet/0000-0003-2304-4869WOS: 000375681800053A theoretical study of resonant tunneling is carried out for an inverse parabolic double-barrier structure subjected to an external electric field. Tunneling transmission coefficient and density of states are analyzed by using the non-equilibrium Green's function approach based on the finite difference method. It is found that the resonant peak of the transmission coefficient, being unity for a symmetrical case, reduces under the applied electric field and depends strongly on the variation of the structure parameters

Spin texturing in a parabolically confined quantum wire with Rashba and Dresselhaus spin-orbit interactions

In this study, we investigate theoretically the effect of spin-orbit coupling on the energy level spectrum and spin texturing of a quantum wire with a parabolic confining potential subjected to the perpendicular magnetic field. Highly accurate numerical calculations have been carried out using a finite element method. Our results reveal that the interplay between the spin-orbit interaction and the effective magnetic field significantly modifies the band structure, producing additional subband extrema and energy gaps. Competing effects between external field and spin-orbit interactions introduce complex features in spin texturing owing to the couplings in energy subbands. We obtain that spatial modulation of the spin density along the wire width can be considerably modified by the spin-orbit coupling strength, magnetic field and charge carrier concentration

Nonlinear optical properties of asymmetric double-graded quantum wells

In this work, the effects of the structure parameters, such as the central barrier thickness and the aluminium concentrations x, on the linear and nonlinear intersubband optical absorption coefficients and refractive index changes of the asymmetric double-graded quantum wells (ADGQWs) under the presence of an external static electric field are studied theoretically. The nonlinear optical properties of the ADGQWs are obtained using the compact-density matrix approach and iterative method. The numerical results obtained from the present work show that the external static electric field and the structure parameters play an important role in the optical properties of ADGQWs. Depending on the asymmetric nature of the confinement potential, in an electric field of <= 20 kV/cm, the overlap between electronic wave functions decreases with increasing field whereas it increases for larger field values. The tunability of intersubband transitions can be applied to optical modulators and various device applications based on the optical transitions of electrons

Energy calculations of quantum dot

We calculated the total energy of a semiconductor quantum dot formed in gate and etching defined devices. A 3D Poisson equation is solved self-consistently to obtain the electron density and potential profile. The total energies of electrons in the quantum dots with two different sizes are calculated with three different approximations by using the density and potential obtained from self-consistent procedure. In our calculation we used a recently developed energy functional called "orbital-free energy functional", Thomas-Fermi approximation and standard local-density approximation within density functional theory. The comparison of these methods reveals the efficacy of the used newly developed orbital-free energy functional which facilitates the calculation of Hartree integral for treatment of electron-electron interaction. (C) 2011 Elsevier B.V. All rights reserved

Nonlinear optical properties of asymmetric double-graded quantum wells

In this work, the effects of the structure parameters, such as the central barrier thickness and the aluminium concentrations x, on the linear and nonlinear intersubband optical absorption coefficients and refractive index changes of the asymmetric double-graded quantum wells (ADGQWs) under the presence of an external static electric field are studied theoretically. The nonlinear optical properties of the ADGQWs are obtained using the compact-density matrix approach and iterative method. The numerical results obtained from the present work show that the external static electric field and the structure parameters play an important role in the optical properties of ADGQWs. Depending on the asymmetric nature of the confinement potential, in an electric field of <= 20 kV/cm, the overlap between electronic wave functions decreases with increasing field whereas it increases for larger field values. The tunability of intersubband transitions can be applied to optical modulators and various device applications based on the optical transitions of electrons