Dispersion Relation in Periodic Potential Band Structure weakly modulated Energy [*(x)] B (-) (+) 2nd band (allowed) e B Dashed line: Free electron Band gap TA 1st band (allowed) + + k 0 T/a 27t/a 1st Brillouin Zone Potential of an atom When k = 'resonance' with lattice occurs (Bragg diffraction of electron by potential with a period of a) Y(+) = e" +e Y(-) = e'a -e Q1: Obtain |Y(+)/2 and (-)|