Each cell is identical and the orbital amplitude is the same in every cell. Only the
phase changes from cell to cell, winding by k·a per step. Drag k from Γ (zone centre)
to the boundary and watch the winding.
k = π/a
phase per cell k·a =
wavelength λ = cells
phase ≈ +1 (real part positive)
phase ≈ −1 (real part negative)
near ±90°
Clocks = the phasor eik·R for each cell. Solid curve = Re ψ(x); dashed = the
fixed amplitude envelope ±|u(x)|, identical in every cell.