  The Abraham momentum of electromagnetic field represents the decomposition
property into real-valued orbital and spin contributions. However, we found
that the orbital and spin momenta of evanescent electromagnetic fields are
inherently complex. Consequently, the decomposition of Abraham momentum was
reexamined and the exact expressions of orbital and spin momenta were obtained,
which are applicable to both propagating and evanescent electromagnetic fields.
Furthermore, we also justified the newly-derived decomposition of Abraham
momentum for lossy media, which was further demonstrated by a concrete example
of surface polariton of metal. In addition, by means of the complex orbital
momentum of surface polariton the complex group velocity was tentatively put
forward with its real part representing the energy flux velocity and its
imaginary part denoting the osmotic velocity of energy penetrating the
corresponding media
