Change of symmetry of the barrierD−ground state in finite magnetic fields

Abstract

The states of the barrier D Ϫ center which consists of a positive ion located on the z axis at a distance from the x-y plane and two electrons in the same plane bound by the ion are investigated based on a direct diagonalization method in finite and relatively high magnetic fields. The energies of the barrier D Ϫ states, the binding energies for the barrier D Ϫ states, and the expectation values of both the distance of the electron from the origin and distance between two electrons are obtained as functions of the applied magnetic field strength ␥ perpendicular to the x-y plane and the distance between the positive ion and the x-y plane. The effects of the higher Landau levels become small as ␥ and increase. The change of symmetry of the barrier D Ϫ ground state is possible in finite magnetic fields. Both the distance of the electron from the origin and distance between two electrons vary discontinuously with the changes of symmetry of the barrier D Ϫ ground states. Our calculations indicate that the phase transitions of the barrier D Ϫ ground states can be observed in real systems.

Transitions of the ground state and electron-electron correlations in barrier centres in magnetic fields

“…The solid lines show the results based on the present variational calculation. To show the accuracy of the present calculation the corresponding results based on the direct diagonalization method in which mixing among the low-lying N mix = 7 Landau levels is taken into account [21] are included in this figure (dotted lines). These results with N mix = 7 are the best results obtained before [21].…”

“…To show the accuracy of the present calculation the corresponding results based on the direct diagonalization method in which mixing among the low-lying N mix = 7 Landau levels is taken into account [21] are included in this figure (dotted lines). These results with N mix = 7 are the best results obtained before [21]. Except for the weak magnetic field for which the results based on the direct diagonalization method are not expected to be accurate, the energies obtained with the present calculation are always higher than those obtained previously.…”

“…They showed that the transitions of the ground state occur between the states with L = 0 ∼ 5 0953-8984/98/204401+12$19.50 c 1998 IOP Publishing Ltd as a function of the distance ζ using the exact solutions for the barrier D − centre in the strong-magnetic-field limit (where −L is the z component of the total angular momentum). In our previous work [21] we investigated the problem of the barrier D − centre based on a direct diagonalization method in which mixing between the different Landau levels is taken into account. We showed that the transitions of the barrier D − ground state also occur in finite magnetic fields.…”

“…It is expected that our variational calculations are accurate in relatively high magnetic fields. The validity of our variational functions will be discussed by comparing the energies of the barrier D − states with those obtained based on the direct diagonalization method [21]. To clarify the mechanism of the transitions of the barrier D − ground state and to have a clear understanding of the electron states of the barrier D − centre, we calculate the binding energies, the electron densities, the angular correlations, and the average distances between the two electrons.…”

Negative-donor centers and absorption spectra of quantum dots

“…A negative-donor center is analogous to the H − ion, which offers an interesting example of a few-particle system where the electron-electron correlation plays a decisive role in trapping and keeping of a second electron [2]. Since the existence of D − centers in center-doped GaAs/Al x Ga 1−x As multiple quantum wells (QWs) was first reported by Huant et al [1] in 1990, many experimental [3][4][5] and theoretical [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] investigations for D − centers in QWs, and quantum dots (QDs) with and without magnetic fields have been carried out. Much of this work has concentrated on GaAs/GaAlAs structures; particularly on isolated nanostructures subjected to an external magnetic field directed perpendicular to the heteroplanes.…”