Hard X-ray RIXS studies of rare earth hexaborides

We present a rare-earth L$_3$ resonant inelastic X-ray scattering f divalent hexaborides RB$_6$ with R=Sm, Yb and compare existing data on X=Eu. In YbB$_6$, we find enhanced RIXS intensity at resonances not near the divalent absorption peak and interpret the nature of the generated excitations with the aid of electronic structure calculations. In addition, we find RIXS signal generated at a well-defined resonance several eV higher that it not observed in absorption and suggest a physical origin of this enhanced resonance-free RIXS signal.