Dynamical Symmetry Breaking under Core Excitation in Graphite: Polarization Correlation in Soft X-Ray Recombination Emission

A recombination emission spectrum is applied to study the local lattice distortion due to core excitation in graphite. The recombination emission spectrum reveals a long low-energy tail when the C $1s$ electron is excited to the ${\sigma }^{*}$ core exciton state. This indicates a large local lattice distortion around the excited carbon atom within a core hole lifetime ($\sim 10\mathrm{f}\mathrm{s}$). A theoretical calculation based upon an ionic cluster model reproduces the experiments well. The strong polarization correlation between incident and emitted x rays is conclusive evidence of symmetry breaking in the core exciton state due to coupling with asymmetric vibrational modes.