Short small-polaron lifetime in the mixed-valence perovskite Cs${}_2$Au${}_2$I${}_6$ from high-pressure pump-probe experiments

Abstract

We study the ultrafast phonon response of mixed-valence perovskite Cs${}_2$Au${}_2$I${}_6$ using pump-probe spectroscopy under high-pressure in a diamond anvil cell. We observed a remarkable softening and broadening of the Au - I stretching phonon mode with both applied pressure and photoexcitation. Using a double-pump scheme we measured a lifetime of the charge transfer excitation into single valence Au${}^{2+}$ of less than 4 ps, which is an indication of the local character of the Au${}^{2+}$ excitation. Furthermore, the strong similarity between the pressure and fluence dependence of the phonon softening shows that the inter-valence charge transfer plays an important role in the structural transition.

arXiv comment4 pages, 4 figures

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