Comment on "Floquet spin states in graphene under ac-driven spin-orbit   interaction"
  A comment on the paper by Lopez et al. [A. Lopez, Z. Z. Sun, and J. Schliemann, Phys. Rev. B 85, 205428 (2012)]. 
Y. Zhou and M. W. Wu
cond-mat.mes-hall cond-mat.mtrl-sci