Abstract:
We report on the observation of an excited 2𝑠 state of a trion in a 4.2 nm wide doped GaAs/Al0.3Ga0.7As quantum well using magneto-optical Kerr effect (MOKE) spectroscopy under out-of-plane magnetic fields up to 6 T. This resonance appears slightly below the 2𝑠 exciton in energy. Strikingly, the 2𝑠 trion is found to be bound only for magnetic fields larger than 1 T. The signature of the 2𝑠 trion is absent in the magnetoreflectance spectra, while it is detectable in the MOKE spectra signifying the importance of the powerful technique. Similar to the 1𝑠 states, the 2𝑠 trion shows an opposite degree of magnetic-field-induced polarization compared to its exciton counterpart, in agreement with our theoretical calculations. This transfer of oscillator strength between the complexes establishes an optical fingerprint of the 2𝑠 excited trion.