Barrier Li Quantum Dots in Magnetic Fields

The methods for the few-body system are introduced to investigate the states of the barrier Li quantum dots (QDs) in an arbitrary strength of magnetic field. The configuration, which consists of a positive ion located on the z-axis at a distaneed from the two-dimensional QD plane (the x-y plane) and three electrons in the dot plane bound by the positive ion, is called a barrier Li center. The system, which consists of three electrons in the dot plane bound by the ion,is called a barrier Li QD. The dependence of energy of the state of the barrier Li QD on an external magnetic field B and the distance d is obtained. The angular momentum L of the ground states is found to jump not only with the variation orB but also with d.     

Effect of the Electron—Phonon Coupling on Barrier D^— Quantum Dots in Magnetic Fields

The influence of the electron-phonon coupling of the energy of low-lying states of the barrier D^- center,which consists of a positive ion located on the z-azis at a distance from the two-dimensional quantum dot plane and two electrons in the dot plane bound by the ion,is investigated at arbitrary strength of maguetic field by mading use of the method of few-body physics.Discontinuous ground-state energy transitions induced by the magnetic field are reported.The dependence of the binding energy of the D^- ground state on the quantum dot radius is obtained.A considerable enhancement of the binding is found for the D^- ground state,which results from the confinement of electrons and electron-phonon coupling.     

Binding Energy of an Exciton Bound to Ionized Acceptor in Quantum Dots

Binding energiesfor an exciton (X) trapped in the two-dimensional quantum dot by a negative ion located on the z axis at a distance from the dot plane are calculated by using the method of few-body physics.This configuration is called a barrier (A^-,X) center.The dependence of the binding energy of the ground state of the barrier (A^-,X)center on the electron-to-hole mass ratio for a few values of the distance d between the fixed negative ion on the z axis and the dot plane is obtained.We find that when d → 0,the barrier (A^-,X) center has not any bound state.We also studied the stability and binding energy of the ground state of the barrier (A^-,X) center in a parabolic quantum dot as a function of the distance d between the fixed negative ion on the z axis and the dot plane.     

Effect of an impurity on 3-electron quantum dots in magnetic fields

1 Introduction Quantum dots (QDs), often referred to as artificial atoms, are currently under in-tense study because they provide ideal structures used in optical-electronic microdevices, so they are essential in developing microtechniques. They are also essential in the aca-demic aspect, because rich information on microstructures can be extracted both theo-retically and experimentally. Since the early fabrication of the QDs, external magnetic field has been used to control their propertie…     

Binding energy of an exciton bound to ionized donors in quantum dots

Binding energies for an exciton (X) trapped in the two-dimensional quantum dot by a positive ion located on the z axis at a distance d from the dot plane are calculated by using the method of few-body physics. This configuration is called a barrier (D⁺,X) center. The dependence of the binding energy of the ground state of the barrier (D⁺,X) center on the dot radius for a few values of the distance d between the fixed positive ion on the z axis and the dot plane is obtained. We find that when d<0.2nm the barrier (D⁺,X) center does not form a bound state.     

Barrier D centers in a quantum disc

The bound states of the barrier D⁻ center, which consists of a positive ion located on the z-axis at a distance λ from the two-dimensional quantum disc plane with a confined parabolic potential and two electrons in the disc plane bound by the ion, are studied under a perpendicular homogeneous magnetic field. The binding energies of the three lowest bound states are calculated as a function of the applied magnetic field strength γ. Discontinuous ground state transitions induced by an external magnetic field have been obtained. We have investigated the effect of the impurity position and found that the transition of the ground-state occurs for finite λ with increasing γ.     

The quantum control of electron states in a double quantum dot under coulomb blocking conditions

The possibility of providing for a quantum control of electron states by means of a weak electric field (constant or alternating) acting upon a system is studied in a nondissipative approximation for a system of two electrons in a double quantum dot (QD) under Coulomb blocking conditions. It is shown that the Coulomb repulsion facilitates controlled transition of the system from a symmetric (one electron in each QD) to asymmetric (both electrons in one QD) electron configuration under the action of a resonance alternating field or a slowly varying (quasi-constant) field. In the absence of Coulomb repulsion, two electrons can be localized in the same QD only under the action of a strong electric field.     

Two-electron states and state exchange time control in parabolic quantum dot

Using the Heisenberg uncertainty relationship and the stationary perturbation theory we consider two-electron states in a spherically symmetric parabolic quantum dot (parabolic helium atom). The dependence of ground-state energy on the QD size is studied. The energy of two-electron system monotonically decreases with QD radius increase. The problem of the state exchange time control in QD is discussed, taking into account the spins of the electrons in the Russell–Saunders approximation. With the increase of the QD radius the state exchange time increases.     

Quantum dot semiconductor laser with optoelectronic feedback

The optoelectronic feedback (OEF) in quantum dot semiconductor lasers (QD SLs) is studied theoretically where a model includes wetting layer ground state and excited state for QDs are included separating electrons and holes in their dynamics. Both positive and negative OEF are studied. The time series of photon density, the phase portraits of carriers in the states are studied. The parameters affecting OEF are examined where an excitability is seen. The QD SL is found to be more sensitive to the changes in time delay compared with other SLs and a complicated routs are seen in the behavior of QD SL.     

Localized charge bifurcation in the coupled quantum dots

We theoretically analyzed localized charge relaxation in a double quantum dot (QD) system coupled with continuous spectrum states in the presence of Coulomb interaction between electrons within a dot. We have found that for a wide range of the system parameters charge relaxation occurs through two stable regimes with significantly different relaxation rates. A certain instant of time exists in the system at which rapid switching between stable regimes takes place. We consider this phenomenon to be applicable for the creation of active elements in nano-electronics based on the fast transition effect between two stable states.     

Doping-enhanced lithium diffusion in lithium-ion batteries

We disclose a distortion-assisted diffusion mechanism in Li3N and Li2.5Co0.5N by first-principles simulations. A B(2g) soft mode at the Γ point is found in α-Li3N, and a more stable α'-Li3N (P3m1) structure, which is 0.71 meV lower in energy, is further derived. The same soft mode is inherited into Li2.5Co0.5N and is enhanced due to Co doping. Consequently, unlike the usual Peierls spin instability along Co-N chains, large lithium-ion displacements on the Li-N plane are induced by a set of soft modes. Such a distortion is expected to offer Li atoms a route to bypass the high diffusion barrier and promote Li-ion conductivity. In addition, we further illustrate abnormal Born effective charges along Co-N chains which result from the competition between the motions of electrons and ion cores. Our results provide future opportunities in both fundamental understanding and structural modifications of Li-ion battery materials.     

Observation of "partial coherence" in an Aharonov-Bohm interferometer with a quantum dot

We report experiments on the interference through spin states of electrons in a quantum dot (QD) embedded in an Aharonov-Bohm (AB) interferometer. We have picked up a spin-pair state, for which the environmental conditions are ideally similar. The AB amplitude is traced in a range of gate voltage that covers the pair. The behavior of the asymmetry in the amplitude around the two Coulomb peaks agrees with the theoretical prediction that the spin-flip process in a QD is related to the quantum dephasing of electrons. These results constitute evidence of "partial coherence" due to an entanglement of spins in the QD and in the interferometer.     

量子点中磁激子的极化子效应

采用推广的LLP方法研究了自组织量子点中磁激子的极化子效应。考虑带电粒子和声子的相互作用,得到了激子能量随磁场的变化关系。结果表明,激子-声子的相互作用降低了激子的能量,但影响很小;极化子效应在没有外磁场时较明显,随着外磁场的增加,这种效应变得越来越弱。     

Vertical magneto-tunneling through a quantum dot and the density of states of small electronic systems

One-electron tunneling through a quantum dot with a strong magnetic field in the direction of the current is studied. The linear magneto-conductance is computed for a model parabolic dot with seven electrons in the intermediate states and for different values of the magnetic field. It is shown that the dot density of states at low excitation energies can be extracted from a precise measurement of the conductance at the upper edge of the Coulomb blockade diamond. We parametrized the density of states with a single “temperature” parameter (in the so called “constant temperature approximation”), and found that this parameter depends very weakly on the magnetic field.     

Controlled dephasing of a quantum dot: from coherent to sequential tunneling

Resonant tunneling through two identical potential barriers renders them transparent, as particle trajectories interfere coherently. Here we realize resonant tunneling in a quantum dot (QD), and show that detection of electron trajectories renders the dot nearly insulating. Measurements were made in the integer quantum Hall regime, with the tunneling electrons in an inner edge channel coupled to detector electrons in a neighboring outer channel, which was partitioned. Quantitative analysis indicates that just a few detector electrons completely dephase the QD.     

Impurity binding energies in quantum dots with parabolic confinement

We present an effective numerical procedure to calculate the binding energies and wave functions of the hydrogen-like impurity states in a quantum dot (QD) with parabolic confinement. The unknown wave function was expressed as an expansion over one-dimensional harmonic oscillator states, which describes the electron's movement along the defined z-axis. Green's function technique used to obtain the solution of Schredinger equation for electronic states in a transverse plane. Binding energy of impurity states is defined as poles of the wave function. The dependences of the binding energy on the position of an impurity, the size of the QD and the magnetic field strength are presented and discussed.     

Influence of a single quantum dot state on the characteristics of a microdisk laser

We report a quantum dot microcavity laser with a cw sub-microW lasing threshold, where a significant reduction of the lasing threshold is observed when a single quantum dot (QD) state is aligned with a cavity mode. The quality factor exceeds 15,000 before the system lases. When no QD states are resonant, below threshold the cavity mode initially degrades with increasing pump power, after which saturation occurs and then the cavity mode recovers. We associate the initial cavity mode spoiling with QD state broadening that occurs with increasing pump power.     

Electronic states of quantum dots: beyond the 2D parabolic model

The quantum states of interacting electrons in a quantum dot in a magnetic field are calculated and the effects of corrections to the 2D parabolic model are examined. The quantum states are obtained by a new method which involves three steps: first the electrostatic potential of the device is obtained from a solution of the Poisson equation, next this potential is used together with a combination of variational and Hartree–Fock calculations to obtain an orthogonal basis whose low-lying states are localised in the region of the dot and finally this basis is used to perform an exact diagonalization. Special attention is paid to the effect of motion perpendicular to the ideal 2D plane and the effect of screening of the Coulomb interaction by metallic electrodes close to the dot. Both effects result in a weakened effective interaction and increase the magnetic fields at which ground-state transitions occur.     

Time-resolved photoluminescence spectroscopy of InAs quantum dots on InP with various InAlGaAs barrier thicknesses

The Optical characteristics of InAs quantum dots (QDs) embeded in InAlGaAs on InP have been investigated by photoluminescence (PL) spectroscopy and time-resolved PL. Four different QD samples are grown by using molecular beam epitaxy, and all the QD samples have five-stacked InAs quantum dot layers with a different InAlGaAs barrier thickness. The PL yield from InAs QDs was increased with an increase in the thickness of the InAlGaAs barrier, and the emission peak positions of all InAs QD samples were measured around 1.5 μm at room temperature. The decay time of the carrier in InAs QDs is decreased abruptly in the QD sample with the 5 nm InAlGaAs barrier. This feature is explained by the tunneling and coupling effect in the vertical direction and probably defect generation.     

Temperature dependence of the properties of strong-coupling bipolaron in a quantum dot

Temperature dependence of the properties of strong-coupling bipolaron in a quantum dot (QD) is studied based on the Lee-Low-Pines-Huybrechts variational method and quantum statistical theory. Results of the numerical calculation show that the vibration frequency as well as the absolute value of the induced potential and the effective potential all increase with increasing coupling strength and temperature, respectively, and they also increase with decreasing relative distance of electrons. The bipolarons are closer and more stable when the temperature is higher and coupling strength is larger. The influence of radius of QD and dielectric constant ratio on the effective potential is little.