Spectral weight A(k,0) on the Fermi surface with d-wave gap anisotropy Δ(φ)=Δ₀cos(2φ)
The pseudogap phase in underdoped cuprates shows gapped antinodal regions (φ≈0) but retains spectral weight near nodes (φ≈π/4) — creating Fermi arcs. The d-wave gap Δ(φ)=Δ₀cos(2φ) vanishes at nodes, where the full Fermi surface is visible. Arc length grows with doping p and T/T* ratio.