  The electronic structure of NdVO3, YVO3 has been investigated as a function
of sample temperature using resonant inelastic soft x-ray scattering at the V
L3-edge. Most of the observed spectral features are in good agreement with an
atomic crystal-field multiplet model. However, a low energy feature is observed
at ~0.4 eV that cannot be explained by crystal-field arguments. The resonant
behaviour of this feature establishes it as due to excitations of the V t2g
states. Moreover, this feature exhibits a strong sample temperature dependence,
reaching maximum intensity in the orbitally-ordered phase of NdVO3, before
becoming suppressed at low temperatures. This behaviour indicates that the
origin of this feature is a collective orbital excitation, i.e. the bi-orbiton.
