Bound polarons in quantum dot quantum well structures

The problem of bound polarons in quantum dot quantum well （QDQW） structures is studied theoretically. The eigenfrequencies of bulk longitudinal optical （LO） and surface optical （SO） modes are derived in the framework of the dielectric continuum approximation. The electron-phonon interaction Hamiltonian for QDQW structures is obtained and the exchange interaction between impurity and LO-phonons is discussed. The binding energy and the trapping energy of the bound polaron in CdS/HgS QDQW structures are calculated. The numerical results reveal that there exist three branches of eigenfrequencies of surface optical vibration in the CdS/HgS QDQW structure. It is also shown that the binding energy and the trapping energy increase as the inner radius of the QDQW structure decreases, with the outer radius fixed, and the trapping energy takes a major part of the binding energy when the inner radius is very small.

Influence of the Interaction Between Phonons and Coulomb Potential on the Properties of a Bound Polaron in a Quantum Dot

The properties of a bound polaron in a parabolic quantum dot with weak electron-LO-phonon coupling under a Coulomb field are studied. The ground state energy of the bound polaron is derived by using a linear combination operator and the perturbation method. The influence of the interaction between phonons with different wave vectors in the recoil process on the ground state energy of the bound polaron is discussed. Numerical calculations are performed,and the results show that the ground state energy increases significantly as the effective confinement length of the quantum dot decreases,considering of the interaction between phonons. When l0〉1.0, the influence of the interaction between phonons on the ground state energy cannot be ignored.

A Fractional-Dimension Variational Approach for the Bound Polaron in Parabolic Quantum Wells

The binding energy of a bound polaron in a finite parabolic quantum well is studied theoretically by a fractional- dimensional variational method. The numerical results for the binding energies of the bound polaron and longitudinal-optical phonon contributions in GaAs/Al0.3 Ga0.7 AS parabolic quantum well structures are obtained as functions of the well width. It is shown that the binding energies of the bound polaron are obviously reduced by the electron-phonon interaction and the phonon contribution is observable and cannot be neglected.

Bound Polaron in a Quantum Well Under an Electric Field

We conduct a theoretical study on the properties of a bound polaron in a quantum well under an electric field using linear combination operator and unitary transformation methods, which are valid in the whole range of electron-LO phonon coupling. The changing relations between the ground-state energy of the bound polaron in the quantum well and the Coulomb bound potential, the electric field strength, and the well width are derived. The numerical results show that the ground-state energy increases with the increase of the electric field strength and the Coulomb bound potential and decreases as the well width increases.

A Polaron in a Quantum Dot quantum Well

The polaron effect in a quantum dot quantum well (QDQW)system is investigated by using the perturbation method. Both the bound electron states outside and inside the shell well are taken into account . Numerical calculation on the CdS/HgS QDQW shows that the phonon correction to the electron ground state energy is quite significant and cannot be neglected.

Temperature and hydrogen-like impurity effects on the excited state of the strong coupling bound polaron in a CsI quantum pseudodot

With hydrogen-like impurity（HLI） located in the center of Cs I quantum pseudodot（QPD） and by using the variational method of Pekar type（VMPT）, we investigate the first-excited state energy（FESE）, excitation energy and transition frequency of the strongly-coupled bound polaron in the present paper. Temperature effects on bound polaron properties are calculated by employing the quantum statistical theory（QST）. According to the present work＇s numerical results, the FESE, excitation energy and transition frequency decay（amplify） with raising temperature in the regime of lower（higher）temperature. They are decreasing functions of Coulomb impurity potential strength.

Polaron effect on the optical rectification in spherical quantum dots with electric field

The polaron effect on the optical rectification in spherical quantum dots with a shallow hydrogenic impurity in the presence of electric field is theoretically investigated by taking into account the interactions of the electrons with both confined and surface optical phonons. Besides, the interaction between impurity and phonons is also considered. Numerical calculations are presented for typical Zn1-xCdxSe/ZnSe material. It is found that the polaronic effect or electric field leads to the redshifted resonant peaks of the optical rectification coefficients. It is also found that the peak values of the optical rectification coefficients with the polaronic effect are larger than without the polaronic effect, especially for smaller Cd concentrations or stronger electric field.

Temperature Effects on the Self-trapping Energy of a Polaron in a GaAs Parabolic Quantum Dot

The temperature and the size dependences of the self-trapping energy of a polaron in a GaAs parabolic quantum dot are investigated by the second order Rayleigh-Schrodinger perturbation method using the framework of the effective mass approximation. The numerical results show that the self-trapping energies of polaron in GaAs parabolic quantum dots shrink with the enhancement of temperature and the size of the quantum dot. The results also indicate that the temperature effect becomes obvious in small quantum dots

Influence of Coulomb Potential on the Properties of a Polaron in a Quantum Dot

The ground-state energy and the average number of virtual phonons around the electron of a hydrogenic impurity confined in a parabolic quantum dot are calculated using the squeezed-state variational approach,which is based on two successive canonical transformations and uses a displaced-oscillator type unitary transformation to deal with the bilinear terms,which are usually neglected.Numerical calculations are carried out in order to study the relation between the ground-state energy and the average number of virtual phonons around the electron of a bound polaron in a parabolic quantum dot with the Coulomb binding parameter.The electron-phonon coupling constant and the confinement length are derived.

Effects of Shannon entropy and electric field on polaron in RbCl triangular quantum dot

In this paper, the time evolution of the quantum mechanical state of a polaron is examined using the Pekar type variational method on the condition of the electric-LO-phonon strong-coupling and polar angle in RbC1 triangular quantum dot. We obtain the eigenenergies, and the eigenfunctions of the ground state, and the first excited state respectively. This system in a quantum dot can be treated as a two-level quantum system qubit and the numerical calculations are performed. The effects of Shannon entropy and electric field on the polaron in the RbC1 triangular quantum dot are also studied.

Magnetpolaron effect in two-dimensional anisotropic parabolic quantum dot in a perpendicular magnetic field

We study the two-dimensional weak-coupling Frohlich polaron in a completely anisotropic quantum dot in a perpendicular magnetic field. By performing a unitary transformation, we first transform the Hamiltonian into a new one which describes an anisotropic harmonic oscillator with new mass and trapping frequencies interacting with the same phonon bath but with different interaction form and strength. Then employing the second-order Rayleigh–Schrodinger perturbation theory, we obtain the polaron correction to the ground-state energy. The magnetic field and anisotropic effects on the polaron correction to the ground-state energy are discussed.

Influence of temperature on ground state energy of bound polaron in asymmetric Gaussian potential quantum well in presence of electromagnetic field

By a combination method of Lee-Low-Pines unitary transformation method and Pekar-type variational method,the ground state energy(GSE)of the bound polaron is studied in the asymmetrical Gaussian potential quantum well considering the temperature and electromagneticfield.The impacts of the temperature and asymmetrical Gaussian potential,electromagnetic field and phonon-electron coupling upon the GSE are obtained.The results show that the GSE of the bound polaron not only oscillates as the temperature changes regardless of the electromagneticfield and asymmetrical Gaussian potential and Coulomb impurity potential(CIP)and electron-phonon coupling but also has different rules with the electromagnetic field and asymmetrical Gaussian potential and CIP and electron-phonon coupling at different temperature zones.

The decoherence of the triangular and Coulomb bound potential quantum dot qubit

We study the eigenenergies and eigenfunctions of the ground and first-excited states of an electron which is strongly coupled to an LO-phonon in a quantum dot with a triangular bound potential and Coulomb bound potential by using the Pekar variational method. This system may be used as a two-level qnbit. Phonon spontaneous emission causes the decoherence of the qubit. Numerical calculations are performed on the decoherence rate as a function of the polar angle, the Coulomb binding parameter, the coupling strength, the confinement length of the quantum dot and the dispersion coefficient.

The ground-state lifetime of polaron in a parabolic quantum dot

This paper reports that the ground-state energy of polaron was obtained with strong electron-LO-phonon coupling by using a variational method of the Pekar type in a parabolic quantum dot. Quantum transition is occurred in the quantum system due to the electron-phonon interaction and the influence of temperature. That is the polaron transit from the ground-state to the first-excited state after absorbing a LO-phonon and it causes the change of the polaron lifetime. Numerical calculations are performed and the results illustrate that the ground-state lifetime of the polaron will increase with increasing the ground-state energy of polaron and decrease with increasing the electron-LO-phonon coupling strength, the confinement length of the quantum dot and the temperature.

Spin Polaron in a Diluted Parabolic Magnetic Quantum Well

Theoretical investigations of spin polaron in a quantum well in the spin doping superlattice systems Cd1-xinMnxinTe/Cd1-xMnxout Te are presented in this paper. A variational procedure within the effective mass approximation is employed in the presence of magnetic field to calculate the donor ionization energy. Spin polaronic shifts are estimated using a mean field theory. The results show that the donor binding energy （i） Increases with the reduction in well sizes （ii） Decreases with the magnetic field is increased for a given well width （ill） Increases to a maximum value at 90 A and then decreases as the size of the well increases beyond 90 A and （iv） Spin polaronic shifts to the donor binding energy not only decrease in a magnetic field but also with the well width. The results are compared with the existing available literature.

Probability density and oscillating period of magnetopolaron in parabolic quantum dot in the presence of Rashba effect and temperature

We study the property of magnetopolaron in a parabolic quantum dot under the Rashba spin–orbit interaction(RSOI)by adopting an unitary transformation of Lee–Low–Pines type and the variational method of Pekar type with and without considering the temperature.The temporal spatial distribution of the probability density and the relationships of the oscillating period with the RSOI constant,confinement constant,electron–phonon coupling strength,phonon wave vector and temperature are discussed.The results show that the probability density of the magnetopolaron in the superposition of the ground and first excited state takes periodic oscillation(T0/period)in the presence or absence of temperature.Because of the RSOI,the oscillating period is divided into different branches.Also,the results indicate that the oscillating period increases(decreases)when the RSOI constant,electron-phonon coupling strength and phonon wave vector(the confinement constant)increase in a proper temperature,and the temperature plays a significant role in determining the properties of the polaron.

Ionized Acceptor Bound Exciton States in Wurtzite GaN/Al_xGa(1-x)N Cylindrical Quantum Dot

Based on the framework of the effective-mass approximation, the ionized acceptor bound exciton （A- X） binding energy and the emission wavelength are investigated for a cylindrical wurtzite （WZ） GaN/A1x Ga1-xN quantum dot （QD） with finite potential barriers by means of a variational method. Numerical results show that the binding energy and the emission wavelength highly depend on the QD size, the position of the ionized acceptor and the Al composition x of the barrier material AIxGal-xN. The binding energy and the emission wavelength are larger when the acceptor is located in the vicinity of the left interface of the QD. In particular, the binding energy of （ A-, X） complex is insensitive to the dot height when the acceptor is located at the left boundary of the QD. The ionized acceptor bound exciton binding energy and the emission wavelength are both increased if Al composition x is increased.

Detection of spin current through a quantum dot with Majorana bound states

The spin transport properties are theoretically investigated when a quantum dot(QD)is side-coupled to Majorana bound states(MBSs)driven by a symmetric dipolar spin battery.It is found that MBSs have a great effect on spin transport properties.The peak-to-valley ratio of the spin current decreases as the coupling strength between the MBS and the QD increases.Moreover,a non-zero charge current with two resonance peaks appears in the system.In the extreme case where the dot-MBS coupling strength is strong enough,the spin current and the charge current are both constants in the non-resonance peak range.When considering the effect of the Zeeman energy,it is interesting that the resonance peak at the higher energy appears one shoulder.And the shoulder turns into a peak when the Zeeman energy is big enough.In addition,the coupling strength between the two MBSs weakens their effects on the currents of the system.These results are helpful for understanding the MBSs signature in the transport spectra.

Effective Mass of Acoustic Polaron in Quantum Dots

The variational effective mass with respect to the e-p coupling constant for different values of cutoff wave vector is performed in quantum dot. The self-trapping transition of acoustic polaron in quantum dot is reconsidered by character of the effective mass curve varying with the e-p coupling. The holes are determined to be self-trapped in AlN quantum dot systems.

Bound polaron in a strained wurtzite GaN/Al_xGa_(1-x)N cylindrical quantum dot

Within the effective-mass approximation,a variational method is adopted to investigate the polaron effect in a strained GaN/Al_xGa_（1-x）N cylindrical quantum dot.The electron couples with both branches of longitudinal optical-like（LO-like）and transverse optical-like（TO-like）phonons and the built-in electric field are taken into account.The numerical results show that the binding energy of the bound polaron is reduced obviously by the polaron effect on the impurity states.Furthermore,the contribution of LO-like phonons to the binding energy is dominant,and the anisotropic angle and Al content influence on the binding energy are small.