Coherent electron dynamics of core-excited molecules at an x-ray free-electron laser*

A new generation of x-ray free-electron lasers (XFELs) offers the possibility to initiate and probe sub-femtosecond electron dynamics in molecules with atomic site specificity. We demonstrate the production of a core-excited electronic wavepacket using isolated attosecond soft x-ray pulses at the Linac Coherent Light Source. We time-resolve the subsequent Auger-Meitner decay process with sub-femtosecond resolution and observe that the evolution of the core-excited wavepacket maps to quantum interference in the emitted Auger-Meitner electron current. Sub-femtosecond precision is achieved by angular streaking and a novel self-referencing scheme. Control of the coherent electron dynamics is achieved by tuning the central photon energy of the exciting XFEL pulse. Mapping the time evolution of the core-excited state to the Auger-Meitner current offers a unique testbed for probing coherent electron dynamics in molecules on the attosecond timescale.