Publication date: 17th July 2025
Photon echo spectroscopy overcomes the significant inhomogeneous broadening of approximately 16 meV in bulk mixed-halide perovskite FA0.9Cs0.1PbI2.8Br0.2 [1], revealing a much narrower homogeneous linewidth of about 16 μeV. This enables direct measurement of the fine structure splitting of excitonic states, arising from the Zeeman effect in an external magnetic field and electron-hole exchange interactions. These splittings manifest as oscillations in the time-resolved photon echo signal, caused by quantum beats between coherently excited exciton states. In Voigt geometry, the applied magnetic field induces mixing between bright and dark exciton eigenstates, allowing us to address and measure the splittings between all four excitonic states. By systematically varying the magnetic field strength and orientation, and combining this with polarization-sensitive excitation and detection, we extract electron and hole g-factors of ge=3.4 and gh=−1.0, respectively, and determine a zero-field splitting of 0.5 meV between the bright (J=1) and dark (J=0) exciton states.
This research was financially supported by the Deutsche Forschungsgemeinschaft (DFG) under project coherent exciton dynamics in lead-free double perovskites. We gratefully acknowledge their support.
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