Measurement of collective excitations in VO$_2$ by resonant inelastic   X-ray scattering
  Vanadium dioxide is of broad interest as a spin-1/2 electron system that realizes a metal-insulator transition near room temperature, due to a combination of strongly correlated and itinerant electron physics. Here, resonant inelastic X-ray scattering is used to measure the excitation spectrum of charge, spin, and lattice degrees of freedom at the vanadium L-edge under different polarization and temperature conditions. These spectra reveal the evolution of energetics across the metal-insulator transition, including the low temperature appearance of a strong candidate for the singlet-triplet excitation of a vanadium dimer. 
Haowei He, A. X. Gray, P. Granitzka, J. W. Jeong, N. P. Aetukuri, R.   Kukreja, Lin Miao, Y. B. Huang, P. Olalde-Velasco, J....
cond-mat.str-el