Magnetic-field dependence of the spin states of the negatively charged exciton in GaAs quantum wells

We present high-field (<50 T) photoluminescence measurements of the binding energy of the singlet and triplet states of the negatively charged exciton in a 200-Angstrom quantum well. Comparing our data with those of other groups and with theoretical predictions we clearly show how the singlet, "bright" and "dark" triplet states may be identified according to the high-field dependence of their binding energies. We demonstrate that a very consistent behavior of the binding energy in a magnetic field has been observed in quantum wells of different widths by different groups and conclude that the triplet state found in this, as well as nearly all other experiments, is undoubtedly the bright triplet. By combining our data with that in the literature we are able to present the generic form of the binding energy of the spin states of the charged exciton in a magnetic field, which reveals the predicted singlet to dark triplet ground state transition at about 20 T

Quantum-mechanical spin states and Zeeman-level diagrams of the positively charged exciton

We consider the spin interaction in the Hamiltonian for the positively charged exciton X+, determining the spin states and Zeeman-level diagrams for X+ in which the heavy- and light-hole bands are degenerate and nondegenerate. The former case results in an X+ with quintuplet and septet states in addition to the singlet and triplet states that are also observed for the negatively charged exciton X-. When the heavy- and light-hole bands are split X+ can comprise two heavy holes, two light holes, or a heavy and a light hole. The heavy-hole X+ Zeeman-level diagram is found to be completely analogous to that of X-, while the light-hole X+ has more optical transitions and a different Zeeman splitting in photoluminescence. X+ consisting of a heavy and a light hole has no coupled hole states, and is truly a heavy- (or light-) hole exciton plus a light (heavy) hole

High-field Zeeman contribution to the trion binding energy

We examine the role of the Zeeman interaction in determining the bound states of the trion at magnetic fields up to 50 T. Polarization-sensitive photoluminescence measurements on the singlet state of the positively charged trion (X+) in GaAs quantum wells demonstrate a 60% enhancement of the g factor compared to that of the neutral exciton (X-0) in the same sample. This leads to a situation in very high fields where the Zeeman splitting of X+ is sufficiently large to determine whether a state is bound or not, and so calls for a reexamination of what is meant by the binding energy of few particle systems

Magnetophotoluminescence of positively-charged excitons in GaAs quantum wells

We have studied the low-temperature photoluminescence of high-mobility two-dimensional hole gases in GaAs quantum wells in magnetic fields up to 50 T. We have observed both spin states of the neutral (X-0) and of the singlet state of the positively charged exciton (X-), allowing us to determine their g-factors and the binding energy of X-. We find that the g-factor of the X is larger than that of X-0 by a factor of 1.6. In very high fields. we expect the low-energy spin-state of X- to be bound only because of the Zeeman interaction. (C) 2002 Elsevier Science B.V. All rights reserved

Experimental observation of the negatively charged exciton stales in high magnetic fields

We have studied the high magnetic field (less than or equal to 50 T) dependence of the negatively charged exciton properties in GaAs/AlxGa1-xAs (x = 0.33) quantum wells using photoluminescence (PL) spectroscopy. Observation of all the optically allowed transitions of the charged exciton allows us to experimentally verify a revised energy-level diagram of spin-split singlet and triplet states. The PL data obtained on all samples are completely consistent with this diagram, leading us to conclude that the negatively charged exciton is a model three-particle system. The binding energy of the negatively charged exciton is measured between 23 and 50 T, and found to be constant for both singlet and triplet states. Our results are compared with recent theory

Energy levels of negatively charged excitons in high magnetic fields

We have studied the photoluminescence energy of the negatively charged exciton for different polarisations in a 100 Angstrom GaAs/ AlGaAs quantum well in magnetic fields up to 50 T. By observing recombination from all of the optically active singlet and triplet states of the charged exciton, we have experimentally determined its energy level diagram. (C) 2000 Elsevier Science Ltd. All rights reserved