Role of doped holes in a U(1) spin liquid
  In the context of the SU(2) slave boson theory we show that condensation of holons can result in the zero mode of a nodal spinon in a single instanton potential. Instanton contribution in the presence of the zero mode induces the 't Hooft effective interaction, here mass to the spinon. We find that the spinon mass is determined by the state of instantons in the presence of the zero mode. The mass corresponds to antiferromagnetic moment of the nodal spinon. Considering the state of instantons, we discuss the possibility of coexistence between antiferromagnetism and $d-wave$ superconductivity in underdoped cuprates. 
Ki-Seok Kim