Jia-Jiong Xiong

Aharonov-Bohm effect of excitons in nanorings

The magnetic field effects on excitons in an InAs nano-ring are studied theoretically. By numerically diagonalizing the effective-mass Hamiltonian of the problem, which can be separated into terms in centre-of-mass and relative coordinates, we calculate the low-lying exciton energy levels and oscillator strengths as a function of the width of the ring and the strength of the external magnetic field. The analytical results are obtained for a narrow-width nano-ring in which the radial motion is the fastest one and adiabatically decoupled from the azimuthal motions. It is shown that in the presence of Coulomb correlation, the so called Aharonov-Bohm effect of excitons exists in a finite (but small) width nano-ring. However, when the ring width becomes large, the non-simply-connected geometry of nano-rings is destroyed and in turn yields the suppression of Aharonov-Bohm effect. The conditional probability distribution calculated for the low-lying exction states allows identification of the presence of Aharonov-Bohm effect. The linear optical susceptibility is also calculated as a function of the magnetic field, to be confronted with the future measurements of optical emission experiments on InAs nano-rings.

Neutral and negative donors in quantum dots

Using a method introduced earlier, the exact solutions of ground states of neutral donor (D0) centres in different quantum dots (QDs) have been obtained, and, taking the Chandrasekhar-type function as a trial function, the ground states of negative donor (D-) centres in QDs have been calculated. The dimensionality and potential-shape effects of QDs on the binding energies EB(D0) and EB(D-) of D0 and D- centres have been studied. The ratio sigma of EB(D0) to EB(D-) has clearly demonstrated the so-called freeze-out effect in different QDs. According to the value of sigma obtained, calculated results of different quantum-well structures can be checked and compared with others. It has been shown that the freeze-out effect and the electron-correlation effect are strongly dependent on the dimensionality of QDs and weakly dependent on the potential shape, and that the polarization term of the trial function not only brings in the important electron-correlation effect but also modifies the behaviour of the single-electron orbitals.

Energy levels and far-infrared spectroscopy for two electrons in a nanoscopic semiconductor ring

The effects of electron-electron interaction of a two-electron nanoring on the energy levels and far-infrared spectroscopy have been investigated based on a model calculation which is performed within the exactly numerical diagonalization. It is found that the interaction changes the energy spectra dramatically, and also shows significant influence on the far-infrared spectroscopy. The crossings between the lowest spin-singlet and triplet states induced by the coulomb interaction are clearly revealed. Our results are related to the experiment recently carried out by A. Lorke et al. [Phys. Rev. Lett. 84, 2223

Low energy exciton states in a nanoscopic semi-conducting ring

We consider an effective mass model for an electron-hole pair in a simplified confinement potential, which is applicable to both a nanoscopic self-assembled semiconducting InAs ring and a quantum dot. The linear optical susceptibility, proportional to the absorption intensity of near-infrared transmission, is calculated as a function of the ring radius

Size effects on excitons in nano-rings

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Properties of electrons and excitons in graded quantum wells of Ga1-xAlxAs in an electric field

. Compared with the properties of the quantum dot corresponding to the model with a very small radius

Confined electron and hydrogenic donor states in a spherical quantum dot of GaAs-Ga1-xAlxAs

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Dimensionality and potential-shape effects on D0 and D- ground states in quantum dots.

, our results are in qualitative agreement with the recent experimental measurements by Pettersson {\it et al}.

Subbands and excitons in GaAs/Ga1-xAlxAs quantum wells with different shapes in an electric field.

The size effects on an exciton in a nano-ring are investigated theoretically by using an effective-mass Hamiltonian which can be separated into terms in centre-of-mass and relative coordinates. The binding energy and oscillator strength of the ground state are calculated for two different ring radii as functions of the ring width. The resulting linear optical susceptibility of the low-lying exciton states is also discussed.

Quantum levels and Zeeman splitting for two-dimensional hydrogenic donor states in a magnetic field

Using the method of series expansion, subbands of electrons and holes, electron-hole overlap functions and binding energies of excitons are calculated for the graded quantum well of Ga1-xAlxAs with a Ga0.66Al0.34As barrier in the electric field F between 0 and +or-9 (104 V cm-1). The width of the well is 200 AA, and the electric field is perpendicular to the material layers. The calculations reveal that the behaviour of electrons and excitons in this well is very different from that in square quantum wells and is useful for some device applications.