In type-II superconductors between H_c1 and H_c2, magnetic flux penetrates as quantized vortices (Φ₀ = h/2e ≈ 2.07×10⁻¹⁵ Wb). Vortices repel and self-organize into a triangular Abrikosov lattice. The superfluid density |ψ|² vanishes at each vortex core.