Akm[k_,m_]:=Piecewise[{{0, k == 0 && m == 0}, {(5*(Sqrt[21]*Ma2u2 + 2*Sqrt[14]*Meu1))/21, k == 2 && m == 0}, {(3/2 - (3*I)/2)*Sqrt[3]*Ma2u1, k == 4 && m == -3}, {(3*(2*Sqrt[21]*Ma2u2 - 3*Sqrt[14]*Meu1))/14, k == 4 && m == 0}, {(-3/2 - (3*I)/2)*Sqrt[3]*Ma2u1, k == 4 && m == 3}}, 0]