The ground state of negatively charged excitons (trions) in high magnetic
fields is shown to be a dark triplet state, confirming long-standing
theoretical predictions. Photoluminescence (PL), reflection, and PL excitation
spectroscopy of CdTe quantum wells reveal that the dark triplet trion has lower
energy than the singlet trion above 24 Tesla. The singlet-triplet crossover is
"hidden" (i.e., the spectral lines themselves do not cross due to different
Zeeman energies), but is confirmed by temperature-dependent PL above and below
24 T. The data also show two bright triplet states.Comment: 4 figure
