I understand the two cases dealt with when we consider the step potential. The two cases being when E>U (i.e the total energy is less than the max potential of the potential barrier) and when E<U. What is the physics of the situation when E=U? Is it a sort of a hybrid situation between the two cases? What would this look like? Classically, the situation is quite clear. If we imagine a marble in a bowl. If E>U, the marble will fall over the lid of the bowl and vice versa if E<U, the marble simply staying put, confined in the bowl. If E=U, the marble just reaches the tip of the bowl, but no more. Quantum mechanically, what does the resulting wavefunction look like?