Room-Temperature Anomalous Coherent Excitonic Optical\nStark Effect in Metal Halide Perovskite Quantum Dots

Abstract

Nonresonant optical driving of confined\nsemiconductors can open\nup exciting opportunities for experimentally realizing strongly interacting\nphoton-dressed (Floquet) states through the optical Stark effect (OSE)\nfor coherent modulation of the exciton state. Here we report the first\nroom-temperature observation of the Floquet biexciton-mediated anomalous\ncoherent excitonic OSE in CsPbBr₃ quantum dots (QDs). Remarkably,\nthe strong exciton–biexciton interaction leads to a coherent\nred shift and splitting of the exciton resonance as a function of\nthe drive photon frequency, similar to Autler–Townes splitting\nin atomic and molecular systems. The large biexciton binding energy\nof ∼71 meV and exciton–biexciton transition dipole moment\nof ∼25 D facilitate the hallmark observations, even at large\ndetuning energies of >300 meV. This is accompanied by an unusual\ncrossover\nfrom linear to nonlinear fluence dependence of the OSE as a function\nof the drive photon frequency. Our findings reveal crucial information\non the unexplored many-body coherent interacting regime, making perovskite\nQDs suitable for room temperature quantum devices.