A New Time-Scale for Tunneling
  We study the tunneling through an oscillating delta barrier. Using time periodicity of the model, the time-dependent Schr\"odinger equation is reduced to a simple but infinite matrix equation. Employing Toeplitz matrices methods, the infinite matrix is replaces by a $3\times 3$ matrix, allowing an analytical solution. Looking at the frequency dependence of the transmissionamplitudes, one observes a new time scale which dominates the tunneling dynamics. This time scale differs from the one previously introduced by B\"uttiker and Landauer. The relation between these two is discussed. 
E. Eisenberg and Y. Ashkenazy