Kondo effect in a quantum antidot

We report Kondo-like behavior in a quantum antidot (a submicron depleted region in a two-dimensional electron gas) in the quantum-Hall regime. When both spins of the lowest Landau level are present all around the antidot, the resonances between extended edge states via antidot bound states show an abnormal feature in alternate Coulomb-blockaded regions. The feature becomes suppressed when the temperature or source-drain bias is raised as for Kondo resonances in quantum dots. Although the exact mechanism is unknown, Kondo-like correlated tunneling may arise from a Skyrmion-type edge reconstruction. This observation demonstrates the generality of the Kondo phenomenon.     

Polarization spectroscopy of positive and negative trions in an InAs quantum dot

Using polarization-sensitive photoluminescence and photoluminescence excitation spectroscopy, we study single InAs/GaAs self-assembled quantum dots. The dots were embedded in an n-type, Schottky diode structure allowing for control of the charge state. We present here the exciton, singly charged exciton (positive and negative trions), and the twice negatively charged exciton. For non-resonant excitation below the wetting layer, we observed a large degree of polarization memory from the radiative recombination of both the positive and negative trions. In excitation spectra, through the p-shell, we have found several sharp resonances in the emission from the s-shell recombination of the dot in all charged states. Some of these excitation resonances exhibit strong coulomb shifts upon addition of charges into the quantum dot. One particular resonance of the negatively charged trion was found to exhibit a fine structure doublet under circular polarization. This observation is explained in terms of resonant absorption into the triplet states of the negative trion.     

Theory of corner reflectors in electron waveguides

The transport properties of corner reflectors have been studied using a method derived from the embedding method for confined quantum systems. The method is used to calculate the eigenstates and Green function which are expanded in any convenient basis set and then used to calculate the transmission and reflection coefficients. The results for the reflectors are compared to the results for a right-angled corner and a circular corner. Current flow studies have been done to clarify the transmission results. The local density of states for the corners are calculated to study bound states and resonances. The reflectors have both one-dimensional and two-dimensional densities of states depending on the size of the reflector.     

The excitation spectrum of quantum antidots

Source-drain bias measurements of transport across quantum antidots reveal a ladder of excited states analogous to the excitation spectrum of quantum dots. The antidot excitation spectrum provides an unambiguous method of determining the Coulomb-blockade charging energy and the energy difference between antidot single-particle states. The energy-level spacings and the presence of strong Kondo resonances in this regime cannot be explained within a non-interacting model.     

Spin-dependent Fano effect through parallel-coupled double quantum dots

Based on the nonequilibrium Green' function method, the spin-dependent Fano effect through parallel-coupled double quantum dots has been investigated by taking account of both Rashba spin-orbit interaction and intradot Coulomb interaction. It is shown that the quantum interference through the bonding, antibonding states and through their Coulomb blockade counterparts may result in two Breit-Wigner resonances and two Fano resonances in the conductance spectra. Moreover, the Fano lineshape of the two spin components can be modulated by Rashba spin-orbit interaction when the magnetic flux is switched on.     

库仑场对抛物量子点中强耦合极化子性质的影响

采用线性组合算符和幺正变换方法研究了在库仑场束缚下抛物量子点中强耦合束缚极化子的振动频率和基态能量。并对其进行了数值计算,结果表明:强耦合束缚极化子的振动频率和基态能量随量子点的有效受限长度的增加而减小,随电子-LO声子耦合强度的增加而增加,束缚极化子的基态能量随库仑势的增加而减小。     

Electroluminescence Caused by the Transport of Interacting Electrons through Parallel Quantum Dots in a Photon Cavity

We show that a Rabi‐splitting of the states of strongly interacting electrons in parallel quantum dots embedded in a short quantum wire placed in a photon cavity can be produced by either the para‐ or the dia‐magnetic electron‐photon interactions when the geometry of the system is properly accounted for and the photon field is tuned close to a resonance with the electron system. We use these two resonances to explore the electroluminescence caused by the transport of electrons through the one‐ and two‐electron ground states of the system and their corresponding conventional and vacuum electroluminescense as the central system is opened up by coupling it to external leads acting as electron reservoirs. Our analysis indicates that high‐order electron‐photon processes are necessary to adequately construct the cavity‐photon dressed electron states needed to describe both types of electroluminescence.     

磁场对非对称量子点中束缚磁极化子性质的影响

采用线性组合算符和幺正变换方法研究磁场对非对称量子点中弱耦合束缚磁极化子性质的影响。导出量子点中弱耦合束缚磁极化子振动频率和基态能量随量子点的横向和纵向有效受限长度、库仑束缚势、磁场的回旋共振频率和电子-声子耦合强度的变化关系。数值计算结果表明:非对称量子点中弱耦合束缚磁极化子的振动频率和基态能量随量子点的横向和纵向有效受限长度的减小而迅速增大。振动频率随库仑束缚势和磁场的回旋共振频率的增加而增大。基态能量随库仑束缚势和电子-声子耦合强度的增加而减小。     

New method for extracting quasi-bound states from the continuum

A new parameter-free method is proposed for treatment of single-particle resonances in the real-energy continuum shell model. This method yields bound states embedded in the continuum, the anamneses of resonances, which provide a natural generalization of weakly bound single-particle states.     

抛物量子点中强耦合束缚磁极化子的性质

采用Pekar类型的变分方法研究了抛物量子点中强耦合束缚磁极化子的基态和激发态的性质.计算了束缚磁极化子的基态和激发态的能量、光学声子平均数以及束缚磁极化子的共振频率.讨论了这些量对回旋频率和有效束缚强度以及库仑束缚势的依赖关系.数值计算结果表明:量子点中强耦合束缚磁极化子的基态能量和共振频率以及光学声子平均数均随量子点的有效束缚强度的增加而减小,基态能量随库仑束缚势的增加而减小,随回旋频率的增加而增大.     

Polarization,spectral, and spatial emission characteristics of chiral semiconductor nanostructures

A detailed study of the degree of circular polarization and the angular dependence of the emission spectra of an array of InAs quantum dots embedded in GaAs photonic nanostructures with chiral symmetry in the absence of an external magnetic field is carried out. A strong angular dependence of the spectra and the degree of circular polarization of radiation from quantum dots, as well as a significant effect of the lattice period of the photonic crystal on the radiation characteristics, is observed. The dispersion of photonic modes near the (±3, 0) and (±2, ±2) Bragg resonances is investigated in detail. The experimentally observed polarization, spectral, and angular characteristics of the quantum-dot emission are explained in the framework of a theory describing radiative processes in chiral photonic nanostructures.     

Correlation between shape and electronic states in nanostructures

We show how the electronic states of quantum wires and quantum dots can be evaluated exactly starting from the profile of the nanostructure observed by transmission electron microscopy, scanning tunneling microscopy and atomic force microscopy. The calculated quantization energies reproduce the energy position of the luminescence resonances in the optical spectra of different samples, without fitting parameters.     

Correlations of conductance peaks and transmission phases in deformed quantum dots

We investigate the Coulomb blockade resonances and the phase of the transmission amplitude of a deformed ballistic quantum dot weakly coupled to leads. We show that preferred single-particle levels exist which stay close to the Fermi energy for a wide range of values of the gate voltage. These states give rise to sequences of Coulomb blockade resonances with correlated peak heights and transmission phases. The correlation of the peak heights becomes stronger with increasing temperature. The phase of the transmission amplitude shows lapses by between the resonances. Implications for recent experiments on ballistic quantum dots are discussed. Received 17 July 1998     

Central potential reconstruction from scattering data by the variable boundary method with the use of Bargmann potentials

An effective numerical method for solving the inverse quantum scattering problem with a fixed angular momentum is suggested. The method is based on combining the variable boundary method suggested earlier and the method of Bargmann potentials. Test calculations are evidence of high method effectiveness in various particular cases, for instance, when there are bound states and resonances.     

Gate-defined graphene quantum point contact in the quantum Hall regime

We investigate transport in a gate-defined graphene quantum point contact in the quantum Hall regime. Edge states confined to the interface of p and n regions in the graphene sheet are controllably brought together from opposite sides of the sample and allowed to mix in this split-gate geometry. Among the expected quantum Hall features, an unexpected additional plateau at 0.5h/e2 is observed. We propose that chaotic mixing of edge channels gives rise to the extra plateau.     

Raman E 1 and E 1 + Δ1 resonances in a system of unstrained germanium quantum dots

The positions and shapes of the Raman E ₁ and E ₁ + Δ₁ resonances of optical phonons are studied as functions of the size of unstrained germanium quantum dots. The quantum dots are grown by molecular-beam epitaxy in GaAs/ZnSe/Ge/ZnSe structures on GaAs(111) wafers. The positions of the E ₁ and E ₁ + Δ₁ resonances are found to shift by at most 0.3 eV. This shift is shown to be well described in terms of a cylindrical model using the quantization of the spectrum of bulk electron-hole states in germanium that form an exciton in a two-dimensional critical point. The fact that the peaks of the E ₁ and E ₁ + Δ₁ resonances appear separately has been detected for the first time, and it is related to the transformation of the interband density of states into a delta function because of spectrum quantization. An increase in the resonance amplitudes in quantum dots as compared to the bulk case is related to the degeneracy multiplicity of the exciton state in the (111) direction.     

抛物量子点中强耦合束缚磁极化子的声子平均数

采用线性组合算符和幺正变换方法导出了强耦合束缚磁极化子的振动频率和声子平均数。讨论了量子点的有效受限长度、磁场、库仑场和电子-LO声子耦合强度对抛物量子点中强耦合束缚磁极化子振动频率和声子平均数的影响。数值计算结果表明:强耦合束缚磁极化子的振动频率和声子平均数均随量子点的有效受限长度、回旋共振频率的增加而减小,随库仑束缚势的增加而增加,声子平均数随电子-LO声子耦合强度增加而减小。     

Optical electron transfer between quantum dots

The continuous spectrum in the problem of resonance optical transitions between bound states of quantum wells is taken into account by the method of equivalence transformation of the initial Hamiltonian. The effective Hamiltonian of resonance interaction, describing the decay of levels to a continuous spectrum, is obtained. The formulas obtained are applied to the problem of resonance electron transfer between quantum dots. The conditions for effective resonance electron transfer are determined.     

磁场和库仑场对抛物量子点中弱耦合极化子激发态性质的影响

采用线性组合算符和幺正变换方法研究了磁场和库仑场对抛物量子点中极化子激发态性质的影响。导出了抛物量子点中弱耦合束缚磁极化子的振动频率、第一内部激发态能量、激发能量与量子点的有效受限长度、库仑束缚势和磁场的回旋频率之间的变化关系。通过数值计算,结果表明:抛物量子点中弱耦合束缚极化子的振动频率、第一内部激发态能量、激发能量均随量子点的有效受限长度减小而迅速增大。随库仑束缚势增大而增大。随磁场的回旋频率的增加而增大。