Figure 3: Dirac potential, strength D
As we discussed in class, in all cases where the potential is finite, the derivatives of the wave functions for the pure energy states, , remain continuous across all boundaries.
If the potential V(x) contains a function at the point x=a of strength D, , then the potential is no longer finite at the point x=a, and there is a discontinuity in the slope. The function, however is not strong enough to generate a discontinuity in the wave function itself.
As we will show in lecture on Thursday, this discontinuity has magnitude
where is the solution to the right of the function (x;SPMgt;a) and is the solution to the left of the function (x;SPMlt;a). We use in the expression (2) because it does not matter which part of the solution one uses for ( wave function is continuous at a: ).