Magnetic field induced donor exciton binding energy in a strained InAs/InP quantum wire

Magneto–exciton bound donor is investigated in a strained InAs/InP quantum wire within the framework of single band effective mass approximation. The strain contribution to the potential is determined via deformation potential theory. The interband optical transition is computed with the various structural parameters in the influence of magnetic field.     

Descending problem in Green's function approach to quantum field theory

The question how to determine lower many-point functions in terms of higher ones, which we call the descending problem, is discussed for the (ø⁴)₁₊₃ model of quantum field theory. Equations to be considered are non-linear non-compact operator equations in complex Banach spaces.Several sufficient sets of conditions for convergence of successive approximation schemes are presented for small values of the renormalised coupling constant. Local uniqueness of solution is proved under certain conditions.     

Magnetic field and finite barrier-height effects on the polarizability of a shallow donor in a GaAs quantum wire

The binding energy and the polarizability are estimated for a shallow donor confined to move in a GaAs quantum well wire (QWW) with a rectangular and square cross-section under the action of an axial magnetic field. In this work, the Hass variational method within the effective mass approximation is used in the case of infinite and finite barrier QWWs. We present our results as a function of the size of the wire and for several values of the magnetic field strength. It is found that the magnetic field strongly reduces the polarizability. The finite barrier-height effect is important for smaller well widths. For higher fields and large wire, the effects of the magnetic field are predominant and the barrier potential is a small perturbation.     

Magnetic field effects on low dimensional electron systems: Luttinger liquid behaviour in a quantum wire

We discuss the effects of a strong magnetic field in quantum wires. We show how the presence of a magnetic field modifies the role played by electron electron interaction producing a strong reduction of the backward scattering corresponding to the Coulomb repulsion. We discuss the consequences of this and other effects of magnetic field on the Tomonaga-Luttinger liquids and especially on their power-law behaviour in all correlation functions. The focal point is the rescaling of all the repulsive terms of the interaction between electrons with opposite momenta, due to the edge localization of the electrons and to the reduction of the length scale. Because of the same two reasons there are some interesting effects of the magnetic field concerning the backward scattering due to the presence of one impurity and the corresponding conductance. As an effect of the magnetic field we find also a spin polarization induced by a combination of electrostatic forces and the Pauli principle, quite similar to the one observed in large Quntum Dots.     

Nonperturbative Green's function approach to quantum field theory and arbitrariness of solutions

Green's function equations are considered for interacting spinor and (pseudo) scalar fields with interactions . These equations do not determine higher many-point functions if two-point functions are given as “input.” If vertex parts are given as input, two-point functions are determined but higher many-point functions are not determined.     

GaAs抛物量子线中弱耦合极化子的磁场效应

应用变分法和改进的线性组合算符法,研究了磁场对抛物量子线中弱耦合极化子振动频率和相互作用能的影响.给出了GaAs抛物量子线中弱耦合极化子的振动频率和相互作用能与磁场和约束强度的依赖关系.对GaAs晶体作了数值计算,结果显示:极化子振动频率和相互作用能都随约束强度和外磁场的增加而增大.     

Magnetic field dependence of the domain wall resistance in a quantum wire

For an ideal one-dimensional ferromagnetic wire with a magnetic domain wall (DW), contribution of the DW to the resistivity of the system has been investigated. We have studied the resistance due to the magnetic impurities in the domain wall which was suspended in a weak magnetic field for two types of chiralities. The analysis has been based on Boltzmann transport equation, within the relaxation time approximation. Through this formalism, both increasing and decreasing of the resistance due to the DW have been predicted in presence of Zeeman interaction as an extrinsic mechanism.     

Volume dependence of the energy spectrum in massive quantum field theories

The low-lying energy values associated to energy eigenstates describing two stable particles enclosed in a (space-like) box of sizeL are shown to be expandable in an asymptotic power series of 1/L. The coefficients in these expansions are related to the appropriate elastic scattering amplitude in a simple and apparently universal manner. At low energies, the scattering amplitude can thus be determined, if an accurate calculation of two-particle energy values is possible (by numerical simulation, for example).     

Magnetic field and symmetry effects in small quantum dots

Shell phenomena in small quantum dots with a few electrons under a perpendicular magnetic field are discussed within a simple model. It is shown that various kinds of shell structures, which occur at specific values for the magnetic field lead to a disappearance of the orbital magnetization for particular magic numbers for noninteracting electrons in small quantum dots. Including the Coulomb interaction between two electrons, we found that the magnetic field gives rise to dynamical symmetries of a three-dimensional axially symmetric two-electron quantum dot with a parabolic confinement. These symmetries manifest themselves as near-degeneracy in the quantum spectrum at specific values of the magnetic field and are robust at any strength of the electron-electron interaction. A remarkable agreement between experimental data and calculations exhibits the important role of the thickness for the two-electron quantum dot for analysis of ground state transitions in a perpendicular magnetic field. The text was submitted by the author in English.     

Carrier energy spectrum and lifetime in quantum dots in electric field

The S-matrix formalism is used to perform analytical calculations of the spectrum of quasi-stationary states of charge carriers in a core-shell quantum dot. Analytical expressions are obtained for the second-order perturbative corrections to the position and half-width of a quasi-stationary energy level, and level shifts are calculated numerically for a core-shell quantum dot in the presence of an electrostatic field. The corrections to level half-width due to Stark effect are analyzed as functions of level energy and barrier thickness. It is shown that there exists a level position E _cr such that the correction δΓ to the level half-width changes sign. An analytical expression for the quadratic Stark shift in a dc-biased quantum well is found in semiclassical approximation. It is shown that the corresponding correction δΓ to half-width also changes sign as energy passes through E _cr. As an example, the Stark shift is calculated for a core-shell quantum dot in the electrostatic field of an adjacent protein molecule.     

Morphology effects of self-assembled quantum dots on the energy spectrum of magneto-excitons

In this paper we analyze the changes experienced by the energy spectra of a confined exciton in type II semiconductor quantum dots, considering the quantum dot as a possible functional part that, in the future devices, can be applied in spintronics, optoelectronics, and quantum information technologies. We studied the lowest energy states of an exciton (X) confined in type II InP/GaInP self-assembled quantum dot (SAQDs), with axial symmetry in the presence of a uniformly applied magnetic field in the growth direction. In our model, it is considered that the electron is located within the point of InP and the hole is in the GaInP barrier. The solution of the Schrödinger equation for this system is obtained by a variational separation process of variables in the adiabatic approximation limit and within the effective mass approximation. We study the energy levels associated with the electron and the hole, and the energy of the exciton. Due to the axial symmetry of the problem the z component of the total orbital angular momentum, L_z=l_e+l_h, is preserved and the exciton states are classified according to the values of this component. Quantum dots have a finite and variable thickness, with the purpose of analyzing the effects related to the variation of the morphology and the presence of a wet layer.     

Adiabatic regularization and Green's function of a scalar field in de Sitter space: Positive energy spectrum and no trace anomaly

In the conventional adiabatic regularization the vacuum ultraviolet divergences of a quantum field in curved spacetime are removed by subtracting the k-mode of the stress tensor to the 4 th-order.For a scalar field in de Sitter space,we find that the4 th-order regularized spectral energy density is negative.Moreover,the 2 nd-order regularization for minimal coupling(ξ=0)and the 0 th-order regularization for conformal coupling(ξ=1/6) yield a positive and UV-convergent spectral energy density and power spectrum.The regularized stress tensor in the vacuum is maximally symmetric and can drive inflation,while its k-modes representing the primordial fluctuations are nonuniformly distributed.Conventional regularization of a Green's function in position space is generally plagued by a log IR divergence.Only in the massless case with ξ=0 or 1/6,we can directly regularize the Green's functions and obtain vanishing results that agree with the adiabatic regularization results.In this case,the regularized power spectrum and stress tensor are both zero,and no trace anomaly exists.To overcome the log IR divergence problem in the massive cases with ξ=0 and 1/6,we perform Fourier transformation of the regularized power spectra and obtain the regularized analytical Green's functions which are IR-and UV-convergent.     

Exact Green's function of the equations of quantum mechanics in an electromagnetic field. I

An exact Green's function of the Cauchy problem in arbitrary (nonparallel) stationary homogeneous electrical and magnetic fields is constructed for the Klein-Gordon-Fock and Dirac equations and for the Pauli equation in arbitrary nonstationary fields, on the basis of a single approach using the method of the canonical Maslov operator (extension of the WKB method to the multidimensional case) and a Fock idea about the proper time in relativitic mechanics.     

Green's function approach to quantum field theory in locally convex space and question of uniqueness

If the set of many point functions ((G ₂ -G ⁰,G ₄, ...,G _N )) satisfies the set of equations arising in the ø⁴ model of quantum field theory, then for a givenG _N the set ((G ₂ -G ⁰,G ₄, ...,G _N-2)), is unique in the domain $$V = \{ ((G_2 - G^0 ,G_4 , \ldots ,G_{N - 2} )) \vdots \left| {((G_2 } \right. - G^0 ,G_4 , \ldots ,G_{N - 2}^{irred} ))\left| {_\iota } \right.< f_l g^{ - {1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} \forall \iota \in \Im \}$$ in a locally convex space equipped with a directed family of semi-norms, wheref _l are positive numbers that depend on details ofG _N , andg?1 is the effective coupling constant.     

Double quantum well electronic energy spectrum within a tilted magnetic field

The analytical solutions of the Schrödinger equation for a double quantum well structure (DQWS) subjected to an externally applied tilted magnetic field are obtained and the results are discussed. The dependency of the energy spectrum of the system on the applied magnetic field direction is also given.     

Simultaneous effects of temperature and pressure on the donor binding energy in a V-groove quantum wire

The influence of temperature and pressure, simultaneously, on the binding energy of a hydrogenic donor impurity in a ridge GaAs/Ga_1−xAl_xAs quantum wire is studied using a variational procedure within the effective mass approximation. The subband energy and the binding energy of the donor impurity in its ground state as a function of the wire bend width and impurity location at different temperatures and pressures are calculated. The results show that, when the temperature increases, the donor binding energy decreases for a constant applied pressure for all wire bend widths. Also, the binding energy increases by increasing the pressure for a constant temperature for all wire bend widths. In addition, when the temperature and pressure are applied simultaneously the binding energy decreases as the quantum wire bend width increases. On the whole, it is deduced that the temperature and pressure have important effects on the donor binding energy in a V-groove quantum wire.     

Internal field relaxation and its effect on the energy spectrum and transport characteristics of a quantum well

We consider internal field relaxation and its effect on the transport characteristics (transmission probability) and the energy spectrum of a quantum well in the context of a modified transfer matrix method. It is shown that the internal field relaxation process leads to the expulsion of the bound state from a quantum well, and to a change in the transport characteristics of such a structure.     

Hyperfunction quantum field theory II. Euclidean Green's functions

The axioms for Euclidean Green's functions are extended to hyperfunction fields without being supplemented by any condition like the linear growth condition of Osterwalder and Schrader.     

Extracting the Green's function from measurements of the energy flux

Existing methods for Green's function extraction give the Green's function from the correlation of field fluctuations recorded at those points. In this work it is shown that the Green's function for acoustic waves can be retrieved from measurements of the integrated energy flux through a closed surface taken from three experiments where two time-harmonic sources first operate separately, and then simultaneously. This makes it possible to infer the Green's function in acoustics from measurements of the energy flux through an arbitrary closed surface surrounding both sources. The theory is also applicable to quantum mechanics where the Green's function can be retrieved from measurement of the flux of scattered particles through a closed surface.