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Institute Methods and Instrumentation for Synchrotron Radiation Research

Charge transfer in matter with Auger Resonant Raman

enlarged view

Through the X-ray excitation an electron is transferred into
a localized state on the excited atom. The wave packet of
the excited electron evolves in time and delocalizes into the substrate.
The charge is transferred.

Charge transfers are one of the key examples for the core-hole clock method. Through the X-ray excitation an electron is transferred from a core state into an excited state that is strongly coupled with the surroundings. By comparing the signal from core decays with the exited electron still present and those, where the excited electron has been transferred to the surroundings allows for an evaluation of the time scale of the charge transfer relative to the time scale of the core decay.

In a typical experiment, the core electron is resonantly transferred into an unoccupied state above the Fermi level. The Auger decays are observed. For an isolated system without charge transfer, the Auger decays will disperse with the excitation energy due to the energy conservation and the lack of dissipation channels. When the system is strongly coupled to the environment, energy dissipative charge transfer can happen and the later decaying Auger electrons will have a constant energy, even if the excitation energy is varied. This different behavior of decays with and without charge transfer as a function of excitation energy makes it easy to disentangle both channels and compare their intensities that yield the average charge transfer time.