Influence of Magnetic Field and LO Phonon Effects on the Spin Polarization State Energy of Strong-Coupling Bipolaron in a Quantum Dot

On the basis of Lee–Low–Pines unitary transformation, the influence of magnetic field and LO phonon effects on the energy of spin polarization states of strong-coupling bipolarons in a quantum dot (QD) is studied by using the variational method of Pekar type. The variations of the ground state energy $E_0$ and the first excited state the energy $E_1$ of bipolarons in a two-dimensional QD with the confinement strength of QDs $\omega _0$ , dielectric constant ratio $\eta $ , electron–phonon coupling strength $\alpha $ and cyclotron resonance frequency of the magnetic field $\omega _{c}$ are derived when the influence of the spin and external magnetic field is taken into account. The results show that both energies of the ground and first excited states ( $E_0$ and $E_1)$ consist of four parts: the single-particle energy of electrons $E_\mathrm{e}$ , Coulomb interaction energy between two electrons $E_\mathrm{c}$ , interaction energy between the electron spin and magnetic field $E_\mathrm{S}$ and interaction energy between the electron and phonon $E_{\mathrm{e-ph}}$ ; the energy level of the first excited state $E_1$ splits into two lines as $E_1^{(1+1)}$ and $E_1^{(1-1)}$ due to the interaction between the single-particle “orbital” motion and magnetic field, and each energy level of the ground and first excited states splits into three “fine structures” caused by the interaction between the electron spin and magnetic field; the value of $E_{\mathrm{e-ph}}$ is always less than zero and its absolute value increases with increasing $\omega _0$ , $\alpha $ and $\omega _c$ ; the effect of the interaction between the electron and phonon is favorable to forming the binding bipolaron, but the existence of the confinement potential and Coulomb repulsive energy between electrons goes against that; the bipolaron with energy $E_1^{(1-1)}$ is easier and more stable in the binding state than that with $E_1^{(1+1)}$ .     

The Polar Optical Phonon Confinement Effect on the Binding Energy of a Hydrogenic Impurity in Quantum Wires Under Applied Electric and Magnetic Fields

The impurity bound polaron in a cylindrical quantum wire with a parabolic confining potential was studied by the variational approach. The polaron effects on the ground-state binding energy in electric and magnetic fields are investigated by means of Pekar-Landau variation technique by taking into account optical phonon confinement within the wire region and localization at its boundaries. It is shown that not only electron confinement, but also polar optical phonon confinement leads to a considerable enhancement of the polaron effect. The results for the binding energy as well as polaronic correction are obtained as a function of the applied fields.     

Electric Field Effect on State Energies and Transition Frequency of a Strong-Coupling Polaron in an Asymmetric Quantum Dot

We study the ground and the first excited states’ energies and the corresponding transition frequency of a strong-coupling polaron in an asymmetric quantum dot (AQD). The effects of the electric field, the transverse and the longitudinal effective confinement lengths and the electron-phonon coupling strength are taken into account by using a variational method of the Pekar type. It is found that the ground and the first excited states’ energies and the transition frequency are decreasing functions of the electric field. They will increase rapidly with decreasing the transverse and longitudinal effective confinement lengths. The transition frequency is an increasing function of the electron-phonon coupling strength, whereas the energies are decreasing ones of it.     

Optical Absorptions of Impurity-Bound Polaron in a GaAs Quantum Dot with Parabolic Potential

The linear and nonlinear optical properties considering polaron and Coulomb impurity effect in a GaAs parabolic quantum dot are investigated theoretically. Calculations have been performed by using the compact density-matrix approach and the Lee-Low-Pines-Huybrecht variational technique for all electron–LO–phonon coupling strengths. The dependence of the optical absorption coefficients on the incident photon energy, the Coulomb potential and incident optical intensity is also studied.     

Rashba Effect on the Bound Polaron in an Asymmetric Quantum Dot

By using LLP variational method, the Rashba effect on the bound polaron in an asymmetric quantum dot is investigated and the expression of the bound polaron ground state energy is derived. Considering different Coulomb bound potentials, we discuss the relations between the ground state energy and the electron–phonon coupling strength, the wave vector, the transverse effective confinement length and the longitudsinal effective confinement length, respectively. The results show that the ground state energy is a decreasing function of the Coulomb bound potential, the electron–phonon coupling strength, the transverse effective confinement length and the longitudinal effective confinement length. On the contrary, it is an increasing function of the wave vector. Due to the Rashba effect, the ground state energy splits into two branches.     

Photon-Assisted Heat Generation in a Quantum Dot Device with the Charging Effect

Electrical current induced heat generation through an ultrasmall quantum dot–leads coupled system under AC fields is investigated by employing the nonequilibrium Green’s function technique. The external AC fields, charging energy and junction capacitances influence the heat generation sensitively. We find negative differential heat generation in our system. The reason for this is the Coulomb interaction, and the negative differential heat generation becomes larger as the frequency of AC fields $\omega $ increases. In addition, the peak caused by charging energy in $Q{/}\omega _0$ curve increases with $\omega $ rapidly. A region in which the value $Q{/}I$ is low emerges due to the charging effect. It is an ideal region for device operation. This region will enlarge as the parameter $R$ and the charging energy $E_c$ increase.     

The Rashba Effect on the Bound Polaron in a Parabolic Quantum Dot

The bound polaron ground state energy is calculated by the variational method of Pekar considering the influence of the Rashba SO interaction on the condition of electric?CLO phonon strong coupling in a parabolic quantum dot (QD). The relations on the bound polaron ground state energy with the parallel confinement length, the electron?CLO phonon coupling constant, the perpendicular confinement length and the Coulomb binding parameter are derived for a parabolic quantum dot.     

Temperature Effect on Effective Mass of the Polaron in an Asymmetric Quantum Dot

We investigate the properties of the polaron in an asymmetric quantum dot by using an improved linear combination operator method. The relations between the mean number of phonons, the effective mass and the temperature are derived. It is found that the mean number of phonons and the effective mass are increasing functions of the temperature.     

The Effects of Hydrogen-Like Impurity and Temperature on State Energies and Transition Frequency of Strong-Coupling Bound Polaron in an Asymmetric Gaussian Potential Quantum Well

In the present work, we study the ground state energy, the first excited state energy and the transition frequency (TF) between the two states of the strong-coupling impurity bound polaron in an asymmetric Gaussian potential quantum well (AGPQW) by using the variational method of the Pekar type. By employing quantum statistics theory, the temperature effect on the state energies (SEs) and the TF are also calculated with a hydrogen-like impurity at the coordinate origin of the AGPQW. According to the obtained results, we found that the SEs and the TF are increasing functions of the temperature, whereas they are decreasing ones of the Coulombic impurity potential.     

The Effect of Magnetic on the Properties of a Parabolic Quantum Dot Qubit

On the condition of electric-LO phonon strong coupling in a parabolic quantum dot, we obtained the eigen energies and the eigenfunctions of the ground state and the first excited state by using the variational method of Pekar type. This system in a quantum dot may be employed as a two-level quantum system qubit. When the electron is in the superposition state of the ground state and the first excited state, we obtained the space-time evolution of the electron density. The relations on the cyclotron frequency with the electron probability density and the period of oscillation are derived in a parabolic quantum dot.     

Suppression of the Kondo Effect in a Quantum Dot by Microwave Radiation

We have studied the influence of microwave radiation on thetransport properties of a semiconductor quantum dot in theKondo regime. In the entire frequency range tested (10–50 GHz), the Kondo resonance vanishes by increasing themicrowave power. This suppression of the Kondo resonance showsan unexpected scaling behavior. No evidence for photon-sideband formation is found. The comparison with temperature-dependence measurements indicates that radiation-induced spindephasing plays an important role in the suppression of theKondo effect.     

Effect of Hyperbolic Band Structure on the Energy Loss Rate of Hot Electrons with Non-equilibrium Phonon Distribution in the Extreme Quantum Limit at Low Temperatures in n-Hg0.8Cd0.2Te

The energy loss rate of hot electrons with the non-equilibrium phonons in narrowgap semiconductors with hyperbolic band structures has been investigated in the extreme quantum limit condition in the low temperature region. The calculation is done for n-Hg_0.8Cd_0.2Te sample considering electron scattering by acoustic phonons via piezoelectric coupling to be the dominant loss mechanism. The value of the energy loss rate with hyperbolic band is compared with the results of parabolic and non-parabolic band structures and at the same time all the results are also compared with the experimentally observed data. It is found that with the inclusion of hyperbolic band structure, the value of energy loss rate is found to be close to the experimental values. The dependence of energy loss rate on magnetic field and lattice temperature has been studied. Using the experimental value of the energy loss rate, the phonon life time is evaluated. The value of the phonon life time is found to be of the order of the phonon boundary relaxation time indicating that phonon boundary scattering is the dominant phonon dissipation mechanism. The dependence of the phonon life time on magnetic field, and lattice temperature has also been studied. The phonon life time is also found to decrease with increase in electron temperature.     

Study of Extensive and Nonextensive Entropy of RbCl Quantum Well Qubit in an Asymmetric Gaussian Potential

Journal of Low Temperature Physics - We have presented extensive and nonextensive entropy of RbCl quantum well qubits (QWQ). To this end, we have considered an electron that is coupled to the...     

Quantum Statistical Properties of Photon and Phonon Fields in Brillouin Scattering with Intense Pumping

The quantum statistical properties of Brillouin scattering of intense laser light are derived including the coupling of Stokes, anti-Stokes and phonon modes, if the anti-Stokes interaction prevails. Making use of the coherent-state technique, the Heisenberg equations of this process are solved neglecting the loss mechanism, and the normal quantum characteristic function and the normal generating function are derived. The time dependences of the photon distribution and its factorial moments are demonstrated if the phonon, Stokes and anti-Stokes modes are initially in a coherent state and periodical anti-bunching of the field is found when the phases of the incident fields fulfil certain phase conditions; the field can also return to the coherent state again.     

Temperature and Impurity Effects of the Polaron in an Anisotropic Quantum Dot

We study the temperature and impurity effects of the ground state energy and the ground state binding energy in an anisotropic quantum dot by using the linear combination operator method. We also discuss the relations of the vibrational frequency and the mean number phonons varying with the Coulomb bound potential at different electron-phonon coupling strength. It is found that the ground state energy and the ground state binding energy will increase with increasing temperature. The ground state energy is a decreasing function of the Coulomb bound potential, whereas the ground state binding energy is an increasing one of it.     

Influences of the Temperature on the Parabolic Quantum Dot Qubit in the Magnetic Field

Using the variational method of the Pekar type, we study the influences of the temperature on the parabolic quantum dot qubit in the magnetic field under the condition of electric–LO-phonon strong coupling. Then we derive the numerical results and formulate the derivative relationships of the oscillation period of the electron in the superposition state of the ground state and the first-excited state with the magnetic field, the electron–LO-phonon coupling constant and the confinement length at different temperatures, respectively.     

温度与加载速率对X70级管线钢韧脆转化现象的影响

在不同温度下测试了X70级管线钢的动态断裂韧度。研究表明:加载速率对动态断裂韧度的影响与温度对其的影响同样重要;在恒温下,增大加载速率可以诱发韧脆断裂转变;当温度由298 K向193 K逐渐降低,或加载速率从0.01 mm/s向1 000 mm/s增大时,均将导致材料的韧脆断裂转变。     

Influence of the Quasiparticle and Phonon Subsystem Coupling on the Multitunneling in STJ Detectors

The scope of this work is to account for the phonon exchange in the process of multitunneling in superconducting tunnel junction (STJ) detector. The theory of branching cascade processes was applied to the process of multitunneling in STJ. The duality nature of quasiparticles and the coupling of the quasiparticle and phonon subsystems were taken into account. The extreme cases of the general formula were analyzed. It was shown that the general formula encloses all specific cases published in literature.