  We investigate how the antiferromagnetic Mott insulator evolves into the
d-wave BCS superconductor through hole doping. Allowing spin fluctuations in
the strong coupling approach, we find a spin-gapped incoherent metal with
preformed pairing as an intermediate phase between the antiferromagnetic Mott
insulator and d-wave superconductor. This non-Fermi liquid metal is identified
with an infrared stable fixed point in the spin-decomposition gauge theory,
analogous to the spin liquid insulator in the slave-boson gauge theory. We
consider the single particle spectrum and dynamical spin susceptibility in the
anomalous metallic phase, and discuss physical implications.
