Definitive observation of the dark triplet ground state of charged excitons in high magnetic fields

TL;DR

This paper experimentally confirms that the ground state of negatively charged excitons (trions) in high magnetic fields is a dark triplet state, aligning with theoretical predictions, through spectroscopic measurements in CdTe quantum wells.

Contribution

It provides the first definitive experimental observation of the dark triplet ground state of charged excitons in high magnetic fields, confirming long-standing theoretical models.

Findings

Dark triplet trion has lower energy than singlet above 24 Tesla

The singlet-triplet crossover is confirmed by temperature-dependent PL

Two bright triplet states are observed

Abstract

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.