There are three curves in this figure.
I use the followed code to fill the gap:
Emin = (6)^2 - (wk + 2)^2; Emax1 = (6)^2; Emax2 = (6)^2 - (wk - 2)^2;
p[x_, left_, right_] :=HeavisideTheta[x - left] HeavisideTheta[right - x];
Plot[{Emin p[wk, 0, 4], Emax1 p[wk, 0, 2], Emax2 p[wk, 2, 4]}, {wk, 0, 4},
Filling -> {1 -> {{2}, {Pink, White}}, 1 -> {{3}, {Pink, White}}}]
Then, I get the figure, which is almost what I want. It would be better if there is no line at the boundary.
How can I fill the gap without the line at the boundary?