Understanding cuprate superconductors with spontaneous nodal gap generation

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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 ξ is zero or less than a critical value ξc 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 ξ 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.