Dielectric enhancement of the exciton energies in laser-dressed near-surface quantum wells

A theoretical study of the intense high-frequency laser field effect on the interband transitions and on the ground (1S-like) and excited (2S-like) exciton states in InGaAs/GaAs near-surface quantum wells is performed within the effective mass approximation. The carrier confinement potentials and image charge contributions to the Coulomb interaction can significantly be modified and controlled by the capped layer thickness and laser field intensity. We found that: (i) the interband and exciton transition energies monotonically enhance with the laser amplitude; (ii) for small capped layers the splitting between the 2S and 1S exciton lines are more sensitive to the dressing laser parameter, and (iii) for high enough laser intensities the dressing effects on both confining potential and Coulomb interactions can yield entirely different exciton emission spectra depending on the cap layer thickness. Our results are compared with the theoretical and experimental data obtained in the absence of the laser field and a good agreement is reached.     

Density of impurity states of shallow donors in a quantum well under intense laser field

The density of donor impurity states in a square GaAs–AlGaAs quantum well under an intense laser field is calculated taking into account the laser dressing effects on both the Coulomb potential and the confining potential. Using the effective-mass approximation within a variational scheme, the donor binding energy is obtained as a function of the laser dressing parameter, and the impurity position. Our results point out that a proper consideration of the density of impurity states may be of relevance in the interpretation of the optical phenomena related to shallow impurities in quantum wells, where the effects of an intense laser field compete with the quantum confinement.     

On the Stability of the Relativistic Electron-Positron Field

We study the energy of relativistic electrons and positrons interacting through the second quantized Coulomb interaction and a self-generated magnetic field. As states we allow generalized Hartree-Fock states in the Fock space. Our main result is the assertion of positivity of the energy, if the atomic numbers and the fine structure constant are not too big. We also discuss the dependence of the result on the dressing of the electrons (choice of subspaces defining the electrons).     

Laser-induced diamagnetic anisotropy of coaxial nanowires

The diamagnetic susceptibility of the hydrogenic impurity in coaxial quantum well wires under high frequency laser field has been investigated taking into account the laser dressing effect on both the impurity Coulomb potential and confinement potential. The analysis revealed that a laser beam which is linearly polarized along the wire radial direction destroys the cylindrical symmetry of the donor Hamiltonian, leading to a strong dependence of the electron probability density on the laser field amplitude and orientation of the applied magnetic field. Thus, the direction of the magnetic field can be used as a tunable parameter in the variation of the diamagnetic susceptibility in low-dimensional structures under intense laser radiation. This phenomenon gives an additional degree of freedom in device applications.     

Perturbation theory for QED bound states

A new method is presented for deriving a systematic perturbative expansion for QED bound states, which does not rely upon solving any new or old equation. The starting point is a given nonperturbative zeroth order Green's function, obtained by a suitable “relativistic dressing” of the nonrelativistic Green's function for the Schrödinger equation with Coulomb potential, which embodies the Coulombic bound states and is known. The comparison with the complete Green's function as given by standard perturbative QED gives a perturbative kernel which is then used for the expansion of the QED Green's function in terms of the given non-perturbative zeroth order Green's function.     

Intense laser effects on donor impurity in a cylindrical single and vertically coupled quantum dots under combined effects of hydrostatic pressure and applied electric field

Using the effective mass and parabolic band approximations and a variational procedure we have calculated the combined effects of intense laser radiation, hydrostatic pressure, and applied electric field on shallow-donor impurity confined in cylindrical-shaped single and double GaAs-Ga_1−xAl_xAs QD. Several impurity positions and inputs of the heterostructure dimensions, hydrostatic pressure, and applied electric field have been considered. The laser effects have been introduced by a perturbative scheme in which the Coulomb and the barrier potentials are modified to obtain dressed potentials. Our findings suggest that (1) for on-center impurities in single QD the binding energy is a decreasing function of the dressing parameter and for small dot dimensions of the structures (lengths and radius) the binding energy is more sensitive to the dressing parameter, (2) the binding energy is an increasing/decreasing function of the hydrostatic pressure/applied electric field, (3) the effects of the intense laser field and applied electric field on the binding energy are dominant over the hydrostatic pressure effects, (4) in vertically coupled QD the binding energy for donor impurity located in the barrier region is smaller than for impurities in the well regions and can be strongly modified by the laser radiation, and finally (5) in asymmetrical double QD heterostructures the binding energy as a function of the impurity positions follows a similar behavior to the observed for the amplitude of probability of the noncorrelated electron wave function.     

Coulomb potentials between spherical heavy ions

The Coulomb interaction between spherical nuclei having arbitrary radial nuclear charge distributions is calculated. All these realistic Coulomb potentials are given in terms of analytical expressions and are available for immediate application. So in no case a numerical computation of the Coulomb integral is required. The parameters of the charge distributions are taken from electron scattering analysis. The Coulomb self-energies of the charge distributions used are also calculated analytically in a closed form. For a number of nucleus-nucleus pairs, the Coulomb potentials derived from realistic charge distributions are compared with those normally used in various nucleus-nucleus optical model calculations. In this connection a detailed discussion of the problem how to choose consistently Coulomb parameters for different approximations is given.     

Cavity‐photon contribution to the effective interaction of electrons in parallel quantum dots

A single cavity photon mode is expected to modify the Coulomb interaction of an electron system in the cavity. Here we investigate this phenomena in a parallel double quantum dot system. We explore properties of the closed system and the system after it has been opened up for electron transport. We show how results for both cases support the idea that the effective electron‐electron interaction becomes more repulsive in the presence of a cavity photon field. This can be understood in terms of the cavity photons dressing the polarization terms in the effective mutual electron interaction leading to nontrivial delocalization or polarization of the charge in the double parallel dot potential. In addition, we find that the effective repulsion of the electrons can be reduced by quadrupolar collective oscillations excited by an external classical dipole electric field.     

Polaronic effects on laser dressed donor impurities in a quantum well

The effect of laser field on the binding energy in a GaAs/Ga1_1−xAl_xAs quantum well within the single band effective mass-approximation is investigated. Exciton binding energy is calculated as a function of well width with the renormalization of the semiconductor gap and conduction valence effective masses. The calculation includes the laser dressing effects on both the impurity Coulomb potential and the confinement potential. The valence-band anisotropy is included in our theoretical model. The 2D Hartree–Fock spatial dielectric function and the polaronic effects have been employed in our calculations. We investigate that reduction of binding energy in a doped quantum well due to screening effect and the intense laser field leads to semiconductor–metal transition.     

The isotropic-to-nematic transition in a two-dimensional fluid of hard needles: a finite-size scaling study

Laser dependence of binding energy on exciton in a GaAs quantum well wire embedded on an AlGaAs wire within the single band effective mass approximation is investigated. Laser dressed donor binding energy is calculated as a function of wire radius with the renormalization of the semiconductor gap and conduction valence effective masses. We take into account the laser dressing effects on both the impurity Coulomb potential and the confinement potential. The valence-band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. The spatial dielectric function and the polaronic effects have been employed in a GaAs/AlGaAs quantum wire. The numerical calculations reveal that the binding energy is found to increase with decrease with the wire radius, and decrease with increase with the value of laser field amplitude, the polaronic effect enhances the binding energy considerably and the binding energy of the impurity for the narrow well wire is more sensitive to the laser field amplitude.     

库仑场对量子线中强耦合极化子性质的影响

采用改进的线性组合算符法研究了库仑场对抛物量子线中强耦合极化子性质的影响。计算了抛物量子线中强耦合束缚极化子的基态能量、振动频率和声子平均数。讨论了这些量对库仑束缚势和约束强度的依赖关系。数值计算结果表明：量子线中强耦合束缚极化子的基态能量随库仑束缚势的增加而减少,随约束强度的增加而增大;振动频率和电子周围的光学声子平均数均随库仑束缚势的增加而增加。     

单电子晶体管电流解析模型及数值分析

本文首先建立单电子晶体管的电流解析模型, 然后将蒙特卡罗法与主方程法结合进行数值分析, 研究了栅极偏压、漏极偏压、温度与隧道结电阻等参数对器件特性的影响. 结果表明: 对于对称结, 库仑台阶随栅极偏压增大而漂移; 漏极电压增大, 库仑振荡振幅增强, 库仑阻塞则衰减; 温度升高将导致库仑台阶和库仑振荡现象消失. 对于非对称结, 源漏隧道结电阻比率增大, 库仑阻塞现象越明显. 关键词： 单电子晶体管 解析模型 蒙特卡罗法 主方程法     

Two- and Three-Body Coulomb Solution Method in a Momentum Space

We present a method to calculate two- and three-body amplitudes including the Coulomb potential in a momentum space. Our aim is to obtain the exact two-body Coulomb amplitudes used in three-body calculations, which reproduce the analytic phase shifts. For the purpose, our theory is based on the modified Coulomb potential (MCP) whose Fourier transformation is equivalent to the pure Coulomb potential in a configuration space, and the two-potential theory with an auxiliary potential. Moreover, one can analytically determine a decisive range R _dec in the MCP. By using the MCP, we obtain the two-body Coulomb modified nuclear amplitude as well as the pure Coulomb amplitude. The calculated phase shift are very good fitting with the experimental data.     

Crystallization in two-component Coulomb systems

The analysis of Coulomb crystallization is extended from one-component to two-component plasmas. Critical parameters for the existence of Coulomb crystals are derived for both classical and quantum crystals. In the latter case, a critical mass ratio of the two charged components is found, which is of the order of 80. Thus, holes in semiconductors with sufficiently flat valence bands are predicted to spontaneously order into a regular lattice. Such hole crystals are intimately related to ion Coulomb crystals in white dwarf and neutron stars as well as to ion crystals produced in the laboratory. A unified phase diagram of two-component Coulomb crystals is presented and is verified by first-principles computer simulations.     

磁场对量子阱中弱耦合束缚极化子性质的影响

采用线性组合算符及幺正变换方法研究了磁场对量子阱中弱耦合束缚极化子的性质的影响。导出了量子阱中束缚极化子的基态能量与振动频率、库仑束缚势、磁场和阱宽之间的变化关系。同时也讨论了振动频率与库仑束缚势、磁场之间的变化关系。通过数值计算结果表明:量子阱中束缚极化子的基态能量因振动频率、库仑束缚势、磁场和阱宽的不同而不同,它随振动频率和磁场的增加而增大,随库仑束缚势和阱宽的增大而减小。量子阱中束缚磁极化子的基态能量与振动频率无关,随库仑束缚势和阱宽的增大而减小,随磁场的增大而增大。     

Single electron transistor with programmable tunnelling structure

A single electron transistor based on the ordered nanodot arrays was reported. The gold nanoparticles self-assembled in the ordered mesoporous silica thin films were used as the Coulomb islands. The Coulomb blockade and Coulomb oscillation are demonstrated at room temperature, and the SIMON simulations are consistent with the experimental results.     

Exponential wave functions for atomic-molecular systems

Geometric properties of correlated exponential basis functions for n-particle Coulomb systems are studied. Using a system of model Schrödinger equations, the relations between the average values of Coulomb interaction energies of pairs of the particles and average values of cosines of the angles of mutual tilt of interparticle bonds are derived. The use of these relations significantly simplifies calculations of the energy operator matrix of many-particle systems by reducing them to evaluation of the Coulomb and normalization integrals. Geometric inequalities are established that allow one to estimate the many-particle Coulomb interaction integrals that are hard to evaluate. The results obtained can be used in calculations of atomic-molecular systems.     

Molecular Dynamics Simulation on Charge Transfer Relaxation between Myoglobin and Water

Dynamical processes of myoglobin after photon-excited charge transfer between Fe ion and surrounding water anion are simulated by a molecular dynamics model. The roles of Coulomb interaction effect and water effect in the relaxation process are discussed. It is found that the relaxations before and after charge transfer are similar. Strong Coulomb interactions and less water mobility decrease Coulomb energy fluctuations. An extra transferred charge of Fe ion has impact on water packing with a distance up to 0.86nm.     

Resonant charge exchange involving highly excited atoms

Transition of a classical electron between two Coulomb centers is analyzed on the basis of computer simulations. The contribution to the electron transfer cross section from a tunnel electron transition is evaluated taking into account the strong mixing of highly excited electron states due to motion of Coulomb centers. The rate of transition of a highly excited electron between two Coulomb cores with a fixed separation is evaluated together with the cross section of resonant charge exchange in slow collisions. Typical times of change of the electron momentum as a result of electron motion in the field of two Coulomb centers are determined. The text was submitted by authors in English.     

Laser dressed donor impurities in free-standing GaAs films under an electric field

The laser-field dependence of the shallow donor states in a free-standing thin GaAs film under an external static field is studied within the effective mass approximation. The laser dressing effects are considered for the confinement potential of the well as well as for the impurity Coulomb interaction distorted by the dielectric mismatch at interfaces. We found that (i) the increase of the laser intensity dramatically modifies the electron potential energy, which establishes the quantum confinement; (ii) the ground state subband energy is significantly enhanced by the electrostatic self-energy arising from the interaction between the electron and its images; (iii) the impurity binding is much larger than those of the dielectrically homogenous case and it becomes stronger sensitive to the laser intensity variation; (iv) under an electric field parallel to the growth direction, the inversion symmetry with respect to the quantum well center is broken and a red/blue-shift of the binding energy, depending on the impurity position along the field direction, occurs. Therefore, the shallow donor energy levels in the free-standing thin films can be tuned in a wide range by proper tailoring of the structure parameters (well size, impurity position) as well as by varying the external applied fields.