Revealing and\nManipulating Hidden Fine-Structure Coherence\nof Bright Excitons in CsPbI<sub>3</sub> Perovskite Quantum Dots

Observation\nand understanding of fine-structure splitting of bright\nexcitons in lead halide perovskite quantum dots (QDs) are crucial\nto their emerging applications in quantum light sources and exciton\ncoherence manipulation. Recent studies demonstrate that ensemble-level\npolarization-resolved transient absorption spectroscopy can reveal\nthe quantum beats arising from the coherence between two fine-structure\nlevels. Here we report the observation of an extra fine-structure\nquantum coherence hidden in previous studies by using cryo-magnetic\nquantum beat spectroscopy. In ∼6 nm CsPbI<sub>3</sub> QDs,\ntwo splitting energies of 0.25 and 1.20 meV were observed at 1.7 K,\nwhich gradually increased to 0.74 and 1.55 meV, respectively, when\na longitudinal magnetic field up to 7 T was applied. The field dependence\nallowed us to extract two distinct nominal Landé <i>g</i>-factors corresponding to QDs with different orientations with respect\nto the external field.