  We study the spontaneous gap generation for gapless nodal fermions within an
effective gauge field theory of high temperature superconductors. When
superconductivity appears, the gauge boson acquires a finite mass via
Anderson-Higgs mechanism. Spontaneous nodal gap generation takes place if the
gauge boson mass $\xi$ is zero or less than a critical value $\xi_{c}$ but is
suppressed by a larger gauge boson mass. The generated nodal gap prohibits the
appearance of low-energy fermion excitations and leads to antiferromagnetic
order. Using the fact that gauge boson mass $\xi$ is proportional to superfluid
density and doping concentration, we build one mechanism that provides a
unified understanding of the finite single particle gap along the nodal
direction in lightly doped cuprates, the competition and coexistence of
antiferromagnetism and superconductivity, and the thermal metal-to-insulator
transition from the superconducting state to the field-induced normal state in
underdoped cuprates.
