为什么Mathematica显示空白框？

Question

我正在尝试绘制Mathematica的功能。但它显示一个空白框

\[Lambda] = -2.5*I;
e0 = .5;
w = .04;
a1 = sqrt[e0^2 - 4*\[Lambda]^2]*(x + t/(4*\[Lambda]^2 - w^2));
h = e0 - 4*I*\[Lambda]*((e0*Sinh[a1] - 2*I*\[Lambda])/(2*I*\[Lambda]*Sinh[a1] + e0));
Plot3D[Abs[h], {x, -2, 2}, {t, -2, 2}]