Parabolic Quantum Wires Research Articles

The effect of Coulomb interaction on optical absorption of a quantum well wire

The optical absorption coefficient in GaAs/AlGaAs cylindrical parabolic quantum wire (QW) with an applied static-electric field is studied in detail. The Schrödinger equation is solved within the effective mass approximation and an analytical solution is used for the electronic structure of cylindrical QW. The main aim is to clarify the effect of the Coulomb interaction on the exciton-related optical absorption of a QW with no assumptions about the strength of the confinement. Finally, it is clearly shown that the further confinement due to Coulomb interaction in a quantum wire increases the transition energy, dipole matrix elements, and absorption peaks, and results with the blue shift. One cannot neglect the Coulomb interaction in the absorption calculations.

Light absorption by free charge carriers in the presence of phonons in an anisotropic quantum wire

The absorption of light by free charge carriers has been theoretically studied considering the processes related to scattering from phonons in an anisotropic parabolic quantum wire. The case in which the electromagnetic wave is polarized along the axis of the wire and the case of non-degenerate electron gas statistics have been considered. In this work, it was determined that the dependence of the location of the peaks of the intraband optical absorption coefficient on the characteristic frequency of the confinement potential in quantum wires with asymmetric parabolic potential was .

Theoretical study of electron compressibility in semiconductor quantum wires

The compressibility was calculated of electrons as a function of external magnetic, temperature and carrier density in the parabolic lateral barrier quantum wires (QWRs). The compressibility found by using Seitz's theorem in which electron self-energy is calculated within the random-phase approximation. All results for GaAs QWRs show that a large difference between the compressibility in low- and high-temperature region at external magnetic fields. These results can help clarify how the Coulomb interaction and exchange, correlation energy affect the compressibility of the semiconductor across a wide range of density, temperature, and external magnetic.

Optical properties of parabolic quantum wires in the presence of electron-electron interactions: An Euler-Lagrange variational application

In this work, we investigate the absorption coefficient and refractive index changes of a parabolic quantum well in the presence of electron-electron interactions. We use a nonlinear term in our Schrödinger equation to simulate the electron-electron interaction effect. We solve the resulting nonlinear Schrödinger equation through an Euler-Lagrange variational method. We study the effects of interaction strength and geometrical potential on energy levels, eigenfunctions, absorption coefficient and refractive index changes. We show that, Electron-electron interaction strength tries to delocalize the wavefunction while geometrical parabolic potential parameter tries to localize it. Thus, by means of these parameters we are able to control the electron confinement and wave function localization. In the literatures, it is usually stated that the electron-electron instructions can be neglected in optical properties investigations. But, when we increase the electron-electron interaction strength from 0 to 1 eV (from null to full electron-electron interaction), the absorption coefficient increases up to 20%, thus it cannot be neglected.

Donor impurity-related photoionization cross-section in parabolic quantum wires: Effects of intense laser field and applied electric field

Within the effective mass approximation, the effects of the electric and intense laser fields on the binding energy and the photoionization cross-section of shallow-donor impurities in GaAs/GaAlAs parabolic quantum wires are investigated theoretically by using a variational method. The numerical results show that the electric and intense laser fields lead to significant changes in the binding energy and photoionization cross-section.

Temperature effect on strong coupling polaron in a parabolic quantum wire in finite well

The ground state energy E0, first excited state energy E1, excitation energy ΔE and oscillating period t of the polaron are calculated by using the linear combination operator and the unitary transformation methods. The variation of the above quantities with the temperature T and the potential well width L, we found that E0, E1and ΔE all increase with increasing T and decrease with increasing L, but t changes with T and L in the opposite.

Rashba效应对量子线中极化子激发态性质的影响

The influence of Rashba effect on properties of excited state of strong-coupling bound polaron in parabolic quantum wires was studied by using of the linear combination operator and the unitary transformation methods.Numerical calculations were performed and the results indicated that they would increase with the increasing of the confinement strength.The excitation energy and the vibrational frequency were increasing functions of the Coulomb bound potential;the first internal excited energy will decrease with the increasing of spin-orbit(SO)coupling strength and the Coulomb bound potential.

有限深势阱下抛物量子线量子比特及其声子效应

有限深势阱下抛物量子线量子比特及其声子效应

The binding energy and structure of biexcitons in quantum wires

This paper describes the use of the finite difference method to study the binding energy and the structure of a biexciton in a model parabolic quantum wire (QWR). The biexciton binding energies calculated for different QWR widths are compared with recent experimental data and reasonable agreement is obtained. The conditional wave function of the biexciton has been investigated, and the structure of a biexciton in a QWR has been found to be similar to that of the H2 molecule. The pair correlation functions for particles in bound biexcitons have also been calculated, and a clear picture for the particle configuration in a biexciton is established. Through the study of the average interparticle distance in a biexciton, we find that the individual excitons may retain their identity in bound biexcitons.

Rashba spin orbit interaction in a quantum wire superlattice

In this work, we study the effects of a longitudinal periodic potential on a parabolic quantum wire defined in a two-dimensional electron gas with Rashba spin-orbit interaction. For an infinite wire superlattice we find, by direct diagonalization, that the energy gaps are shifted away from the usual Bragg planes due to the Rashba spin-orbit interaction. Interestingly, our results show that the location of the band gaps in energy can be controlled via the strength of the Rashba spin-orbit interaction. We have also calculated the charge conductance through a periodic potential of a finite length via the nonequilibrium Green's function method combined with the Landauer formalism. We find dips in the conductance that correspond well to the energy gaps of the infinite wire superlattice. From the infinite wire energy dispersion, we derive an equation relating the location of the conductance dips as a function of the (gate controllable) Fermi energy to the Rashba spin-orbit coupling strength. We propose that the strength of the Rashba spin-orbit interaction can be extracted via a charge conductance measurement.

Exciton binding energy and excitonic absorption spectra in a parabolic quantum wire under transverse electric field

The effects of transverse electric field on the energy levels of electron and heavy hole, exciton binding energy and excitonic absorption spectra of GaAs parabolic quantum wire are theoretically investigated in detail. The results indicate that the electron and hole energy levels, exciton binding energy, excitonic absorption coefficient and absorption energy becomes smaller with the increase of electric field. That is more significant at the condition of weaker parabolic confinement potential. The phenomena can be explained by the separation of overlap integral of the electron and hole at the ground states.

Polaron effects on the binding energy of a hydrogenic impurity in parabolic quantum wires in perpendicular electric and magnetic fields

Using a variational approach, the binding energy of shallow hydrogenic impurities in a parabolic quantum wire is calculated within the effective mass approximation. The polaron effects on the ground-state binding energy in electric and magnetic fields are investigated by means of the Pekar–Landau variation technique. The results for the binding energy as well as a polaronic correction are obtained as a function of the applied fields and the impurity positions.

Coulomb interaction and transient charging of excited states in open nanosystems

We obtain and analyze the effect of electron-electron Coulomb interaction on the time dependent current flowing through a mesoscopic system connected to biased semi-infinite leads. We assume the contact is gradually switched on in time and we calculate the time dependent reduced density operator of the sample using the generalized master equation. The many-electron states (MES) of the isolated sample are derived with the exact diagonalization method. The chemical potentials of the two leads create a bias window which determines which MES are relevant to the charging and discharging of the sample and to the currents, during the transient or steady states. We discuss the contribution of the MES with fixed number of electrons N and we find that in the transient regime there are excited states more active than the ground state even for N=1. This is a dynamical signature of the Coulomb blockade phenomenon. We discuss numerical results for three sample models: short 1D chain, 2D lattice, and 2D parabolic quantum wire.

Time-dependent transport via the generalized master equation through a finite quantum wire with an embedded subsystem

In this paper, we apply the generalized master equation to analyze time-dependent transport through a finite quantum wire with an embedded subsystem. The parabolic quantum wire and the leads with several subbands are described by a continuous model. We use an approach originally developed for a tight-binding description selecting the relevant states for transport around the bias-window defined around the values of the chemical potential in the left and right leads in order to capture the effects of the nontrivial geometry of the system in the transport. We observe a partial current reflection as a manifestation of a quasi-bound state in an embedded well and the formation of a resonance state between an off-set potential hill and the boundary of the system.

Energy dispersion of the electrosubbands in parabolic confining quantum wires:interplay of Rashba, Dresselhaus, lateral spin–orbit interaction and the Zeemaneffect

We have made a thorough theoretical investigation of the interplay of spin–orbitinteractions (SOIs) resulting from Rashba, Dresselhaus and the lateral parabolic confiningpotential on the energy dispersion relation of the spin subbands in a parabolic quantumwire. The influence of an applied external magnetic field is also discussed. We show theinterplay of different types of SOI, as well as the Zeeman effect, leads to rather complexand intriguing electrosubbands for different spin branches. The effect of differentcoupling strengths and different magnetic field strengths is also investigated.

Modeling of Coulomb interaction in parabolic quantum wires

We study the exciton states in a parabolic quantum wire. An exactly solvable model is introduced for calculating the exciton state and the binding energy as a function of the radius of the quantum wire within the envelope-function approximation. In the calculation, we replace the actual Coulomb interaction between the electron and the hole by a Gaussian nonlocal separable potential and obtain closed expressions for both the envelope-function and the binding energy. Results are compared with those obtained by perturbative methods.

Transient magnetotransport through a quantum wire

We consider an ideal parabolic quantum wire in a perpendicular magnetic field. A simple Gaussian-shaped scattering potential well or hill is flashed softly on and off with its maximum at $t=0$, mimicking a temporary broadening or narrowing of the wire. By an extension of the Lippmann-Schwinger formalism to time-dependent scattering potentials, we investigate the effects on the continuous current that is driven through the quantum wire with a vanishingly small forward bias. The Lippmann-Schwinger approach to the scattering process enables us to investigate the interplay between geometrical effects and effects caused by the magnetic field.

Third-harmonic generation in cylindrical parabolic quantum wires with static magnetic fields

The third-harmonic generation (THG) and its conversion efficiency in Al x Ga 1 - x As / GaAs cylindrical parabolic quantum wires with static magnetic fields are studied in detail. The calculated results show that the parabolic confining potential and the static magnetic field have evident influence on the THG and its conversion efficiency. In addition, the conversion efficiency of the THG is also related to the input optical intensity. It is noted that very high conversion efficiency of the THG can be obtained by increasing properly the input optical intensity and choosing an optimized parabolic confining potential and applied static magnetic field.

Spin densities in parabolic quantum wires with Rashba spin‐orbit interaction

Using canonical transformations we diagonalize approximately the Hamiltonian of a gaussian wire with Rashba spin-orbit interaction. This proceedure allows us to obtain the energy dispersion relations and the wavefunctions with good accuracy, even in systems with relatively strong Rashba coupling. With these eigenstates one can calculate the non-equilibrium spin densities induced by applying bias voltages across the sample. We focus on the z -component of the spin density, which is related to the spin Hall effect. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Third-harmonic generation in cylindrical parabolic quantum wires with an applied electric field

The third-harmonic generation (THG) in $\mathrm{GaAs}∕\mathrm{AlGaAs}$ cylindrical parabolic quantum wires with an applied static-electric field is studied in detail. An analytic formula for the THG susceptibility in the model is obtained by a compact density matrix approach and an iterative procedure. Finally, the calculated results show the parabolic confinement potential and the applied electric field have great influence on the THG susceptibilities in the system. Another important point is that the maximum THG susceptibility over ${10}^{\ensuremath{-}9}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}∕{\mathrm{V}}^{2}$ can be obtained by optimizing the parabolic confinement potential and the applied electric field, which is over ten orders of magnitude greater than in bulk GaAs. The contributors to the very giant three-order nonlinear include the very large dipole transition matrixes and the triple resonant condition.