Time-Resolved RIXS / REXS

Resonant Inelastic / Elastic X-Ray Scattering (RIXS / REXS) is a powerful technique to probe the momentum-resolved electronic structures of materials with a high level of details. The RIXS / REXS process starts with an x-ray absorption process: by tuning the incoming x-ray resonant to an elemental edge, the core-level electrons will be excited to an unoccupied state above the Fermi level, leaving behind core holes. The system then responds to this excited state in several possible ways:

  1. The excited electrons recombine with the core holes without transferring energy into the system, resulting in the elastic scattering of the x-rays (REXS) that can be used to probe the charge ordering and symmetries of the material.
  2. The valence electrons below the Fermi level recombine with the core holes instead, emitting outgoing x-rays with energies lower than the incoming x-rays (energy loss / transfer), resulting in inelastic scattering of the x-rays (RIXS) that can be used to probe the charge-transfer and orbital excitations of the material.
  3. The excited electrons further excite quasi-particles such as phonons and magnons in the material, emitting outgoing x-rays with energies also lower than the incoming x-rays (RIXS). As the energy loss is equal to the characteristic energies of the excited quasi-particles, this allows for the investigation of the vibrational and magnetic characteristics of the material.
  4. Pump-probe time-resolved RIXS / REXS (tr-RIXS / tr-REXS) adds another dimension to the technique by introducing an additional energy perturbation in the form of pulsed-laser pump. This allows for the time-resolved investigation of the material already in an excited / perturbed state, which can uncover the coupling dynamics between the various degrees of freedom in the material. The additional energy may also cause the outgoing x-rays to be higher in energy than the incoming x-rays, resulting in energy-gaining excitations not found in the ground state of the material at equilibrium.

At SCS, time-resolved RIXS / REXS can be performed by coupling the CHEM or XRD chamber to the hRIXS spectrometer.

 

Further reading: T. C. Asmara et al., Adv. Mater. 36, 2310668 (2024).