Crossing behavior of the singlet and triplet state of the negatively charged magnetoexciton in a GaAs/Al0.55Ga0.45As quantum well

Polarized magnetophotoluminescence (MPL) measurements on a high-mobility de lta-doped GaAs/Al0.55Ga0.45As single quantum well from 0 to 60 T at tempera tures between 0.37 and 2.1 K are reported. In addition to the neutral heavy -hole magnetoexciton (X-0), the singlet (X-s(-)) and tripler (X-t(-)) state s of the negatively charged magnetoexciton are observed in both polarizatio ns. The energy-dispersive and time-resolved MPL data suggest that their dev elopment is fundamentally related to the formation of the neutral magnetoex citon. At a magnetic field of 40 T the singlet and the triplet states cross as a result of the role played by the higher Landau levels and higher-ener gy subbands in their energetic evolution, confirming theoretical prediction s. We also observed the formation of two higher-energy peaks. One of them i s completely right circularly polarized and its appearance can be considere d a result of the electron-hole exchange interaction enhancement with an as sociated electron g factor of 3.7 times the bull; value. The other peak com pletely dominates the MPL spectrum at fields around 30 T. Its behavior with magnetic field and temperature indicates that it may be related to previou s anomalies observed in the integer and fractional quantum Hall regimes.