Resonant Inelastic X-Ray Scattering as a Probe of the Phase and   Excitations of the Order Parameter of Superconductors
  The capability to probe the dispersion of elementary spin, charge, orbital, and lattice excitations has positioned resonant inelastic x-ray scattering (RIXS) at the forefront of photon science. Here we develop the scattering theory for RIXS on superconductors, calculating its momentum-dependent scattering amplitude. Considering superconductors with different pairing symmetries, we show that the low-energy scattering is strongly affected by the superconducting gap and coherence factors. This establishes RIXS as a tool to disentangle pairing symmetries and to probe the elementary excitations of unconventional superconductors. 
Pasquale Marra, Steffen Sykora, Krzysztof Wohlfeld, Jeroen van den   Brink
cond-mat.supr-con cond-mat.str-el