3.3 Solutions 197
Fig. 3.19Class I and Class II wave functions
3.49 The analysis for the reflection and transmission of stream of particles from
the square well potential is similar to that for a barrier (Problem 3.30) except
that the potentialVbmust be replaced by−V 0 and in the region 2,k 2 must be
replaced byik 2. Thus, from Eq. (9) of Problem 3.30, we get
τ=
4 k 1 k 2 exp(−ik 1 a)
(k 2 +k 1 )^2 exp(−ik 2 a)−(k 2 −k 1 )^2 exp(ik 2 a)
The fraction of transmitted particles whenk 2 a=nπis determined by the
imaginary exponential terms in the denominator.
e+inπ=cosnπ±isin(nπ)=cosnπ
=1; (n= 0 , 2 , 4 ·)
=−1; (n= 1 , 3 , 5 ...)
Fig. 3.20Transmission
coefficientTas a function of
the ratioE/Vofor attractive
square well potential
Thereforeτ∗= 1
A typical graph forTas a function ofE/V 0 is shown in Fig. 3.20.
In general we get the transmission coefficient
T=
∣
∣
∣
∣
∣
1 +
V 02 sin^2 k 2 a
4 E(E+V 0 )
∣
∣
∣
∣
∣
− 1
The transmission coefficient goes to zero atE=0 because of the 1/Eterm
in the denominator. ForE/V 0 1, narrow transmission bands occur when-