  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.
